This paper, based on historical land area and population in China, calculates the maximum land area for one rural labor under “labor matching with employment” at traditional plowing modes, and estimates the minimum labors for farmland to load in 2008, 2020 and 2030 at multicropping index 1, 1.26 and multi-cropping index 1.26 & minimum operation, the surplus labor needs to migrate to cities. This paper, according to urban planning standards, works out the total urban construction land area and land area to be occupied. The rural residence left by farmers who migrate to cities, after rehabilitation, can be used for added land area, which is balanced with occupied construction land area. The both are used to calculate the preserved farmland area in China.