Abstract: The farmland classification precision depends on the PRC(productive ratio coefficient) calculation. According to the standard of the farmland classification method in China, the PRC was calculated by the rate of the base crop yeild maximum and the appointed crop yield maximum, but, for the impacts of the different PRC calculation methods on the farmland classification precision was unknown. The PRC calculation methods' improvement is base of the national farmland classification standard. In the paper, Chongming county in Shangha was taken as a case study, the other five PRC calculation methods except for the standard method were brought out, to show the impacts on the farmland classification precision. The results show that the different PRC can increase or decrease the natural quality grade, utilization grade index on the whole, but, grade spatial distribution orders of the relative farmland were the same. In the same cropping system, the six PRC calculation methods have the same impacts on the farmland classification precision, but the farmland index based on the different PRC has the same agricultural productivity.