In this experiment, straw, edible fungus residue and sawdust were mixed with different volumes of paddy soil as machine substrate, and the effects of different substrates, composting and composting on the growth, root system and yield of plug seedlings of multiple cropping machine were studied. The results are as follows: (1) The rice seedling substrate made of rice straw, bacteria, sawdust and soil has light texture and high porosity, and the root system of seedlings grows and develops, and the number of roots per seedling is more than that of paddy soil substrate. (2) After retting the straw substrate, the substrate and fertilizer are better blended, and the substrate is soft, which is beneficial to the growth of seedlings. The high germination rate increased by 4.79% to 4.79%, and the number of seedlings, roots and dry weight of seedlings were better than those without composting, with good quality. (3) 300 g compound fertilizer was added to every 100 liter of seedling matrix, and it was not piled up. 1) added three kinds of substrate substances, and the stem base width, dry weight per plant, root-shoot ratio and leaf age of early rice seedlings were weaker than those of paddy soil, becoming short seedlings and the quality of seedlings declined. After transplanting Honda, it took a long time to turn green and tillered slowly, and began to reduce production. (2) With the increase of the proportion of raw materials, the quality of seedlings became worse, and the proportion of 1: 1 was better, while the proportion of 3- 1 and the substrate filled with sawdust was better. When the yield and ratio are 3: 1, the comprehensive performance of wood substrate is the best. (3) The seedling quality of late rice in the field is better than that of the control treatment, with strong rooting ability in the field, fast tillering after planting, strong vigor and high panicle rate. The yield was lower than that of paddy soil except straw 3: 1 and 1:3. (4) On the premise that 600g of compound fertilizer is mixed into every100l of seedling matrix, and the compost is sufficient. Straw substrate is higher than paddy soil, seedling emergence rate and seedling height, stem width, root number and starch content of sawdust substrate seedlings are better than the control, and the quality advantage is obvious. And the bacterial quality of seedlings and paddy soil. (5) With the increase of nitrogen application rate, the leaf age of early rice seedlings increased, and there was a significant difference between N5 and N 1, and their long leaf sheaths gradually increased, but the growth effect was not obvious with the increase of nitrogen application rate. The seedling rate, seedling height, stem width, leaf SPDA value, plant leaf, root dry weight and field rooting ability decreased first and then increased. The seedlings with low soluble sugar content are treated with low-fat M ore, and the amount of nitrogen fertilizer is too much, which is not conducive to the accumulation of soluble sugar. The comprehensive performance of N3 is the best, and the quality of N2 N4 is also good. (6) Fertilizing with urea produces ammonia gas, the top dressing time is short, the amount of fertilizer is increased, the cultivation is easy to cause bud burning, the rice seedling emergence is unfavorable, the seedling emergence rate is reduced, the seedlings are leaked, and the machine quality is reduced. Therefore, fertilizer should be applied as soon as possible in production, instead of using urea fertilizer. (7) After transplanting Honda and increasing nitrogen content, early tillering started quickly, and the number of tillers was earlier, which ensured sufficient panicles and increased effective panicles. The yield of N3 early rice was the highest, and N4 interchange was the highest in late rice. To sum up, using rice straw, sawdust, fungus chaff and other basic materials to partially or completely replace paddy soil as substrate, appropriate fertilizer dosage and sufficient retting can provide better growth conditions for rice seedlings than paddy soil substrate, and can cultivate more robust mechanical plug seedlings, and the volume ratio is 3: 1. The volume ratio of rice straw and paddy soil is 3∶ 1, and the appropriate nitrogen application rate is 90 ~100g per100l. Key words: mechanical transplanting, seedling substrate, nitrogen application rate, seedling quality, yield