Abstract: The field experiment was conducted to investigate the requirements of irrigation and nitrogen fertilizer to increase wheat yield under straw mulch after the models of yield were created. The results showed that the increase of yield depended greatly on N fertilizer and irrigation water when straw mulch was applied. If no irrigation water was supplied, the increase of yield in straw-mulch treatment depended on the amount of N fertilizer. The yield of straw-mulch treatment was much higher than that of no-mulch treatment when 240 kg/hm² N fertilizer was applied. The reverse was true when too much N fertilizer was applied. Higher wheat yield under straw mulch could be reached in rainfed areas based on appropriate N fertilizer. The increase of yield depended on the distribution of irrigation water at the different stages of wheat growth as well as the total amount of irrigation water when amount of N fertilizer was a constant. A water-saving way to obtain higher yield is to distribute the limited irrigation water to the key stage of wheat growth based on the N fertilizer when irrigation is available.