With a laboratory simulation experiment, the responses of soil dissolved nitrogen (Dissolved inorganic nitrogen, DIN; Dissolved organic nitrogen, DON; Dissolved total nitrogen, DTN) content, microbial biomass nitrogen (MBN) content and net nitrogen mineralization rate (NNMR) to different freezing-thawing temperatures and freezing-thawing frequencies were studied in a farmland brown soil. The results showed that freezing temperature and freezing-thawing frequency were the major factors affecting N transformation process of farmland brown soil. With freezing temperature decreasing, NO₃^– -N,NH₄⁺ -N, DIN, DON, DTN and NNMR all significantly increased, but MBN first decreased then increased. With freezing-thawing frequency increasing, NO₃^– -N, NH₄⁺ -N, DIN and DTN all significantly increased being contrary to the changes of NNMR, and MBN showed a trend of decrease-increase-decrease being contrary to the changes of DON. Therefore, it was preliminarily concluded that freezing-thawing cycle significantly promoted N transformation of farmland brown soil during no growth season, and further increased soil DIN content and soil N supply capacity.