3000 yuan. There are four people in the family, and the annual household income 12000 can be lowered. However, the per capita annual income cannot be lower than 1800 yuan, because 1800 yuan belongs to the extreme poverty line. The standard of the average annual income of poor students varies according to the economic situation of different regions and countries, and the specific amount should be determined according to the local living costs and social welfare standards. Therefore, it is more appropriate for poor families to write an annual income of 3000 yuan.