The so-called ratchet effect means that people's consumption habits are irreversible after they are formed, that is, it is easy to adjust upwards and difficult to adjust downwards. Especially in the short term, consumption is irreversible and the habitual effect is great. This habit effect makes consumption depend on relative income, that is, relative to its past peak income. It is easy for consumers to increase consumption with the increase of income, but it is not easy to reduce consumption with the decrease of income, thus producing a short-term consumption function with positive intercept. This characteristic is called ratchet effect.