Abstract: Mechanism for mitigating soil acidification in croplands were proposed on the basis of alkalinity of organic manures calculated with an element analysis method and compared with relevant reference data, and then factors affecting manure alkalinity were discussed in this paper. Results showed that the alkalinity of different organic manures ranged in 58.1372.8 cmol/kg and the corresponding CaCO3 equivalent ranged in 29.0186.4 g/kg. The increase of alkalinity was in the order of cereal straw legume straw green manure fresh dung common straw compost thermophilic straw compost barnyard manure. The alkalinity significantly positively correlated with the calcium content (r =0.98, P 0.001, n =32), but significantly negatively correlated with the carbon content (r = 0.64, P 0.001, n =32) in the organic materials, and was mainly determined by the equivalent content of organic acid salts. The output of agricultural product and input of organic manure were two inter-reciprocal processes to soil acidification in croplands. Long-term manure application could offset the loss of soil base minerals through biomass removal. Application of organic manure with high alkalinity (e.g. thermophilic straw compost or barnyard manure) not only could mitigate soil acidification in croplands, but also reduced application costs and improved the resource utilization rate of organic manure.