A field experiment was conducted on a Hongyou soil of Yangling to investigate the effects of irrigation and nitrogen fertilization on wheat yield under straw mulch. The results showed that under straw mulch, N fertilization contributed more to the increase of wheat yield than irrigation, because soil moisture condition was improved greatly. The interaction between irrigation and nitrogen fertilization was negative in no-mulch treatment, but positive under straw mulch. For dryland, more attention should be paid to the input of nutrients when straw mulch was applied. High moisture content in soil profile before sowing and sufficient N input were essential for good harvest when field was not mulched. Under straw mulch, the irrigation rate for a maximum yield was reduced, and the optimum time of irrigation was postponed. Wheat grain yield had no relation to the irrigation during jointing stage in both no-mulch and straw mulch treatments.