A 24-year fertilization experiment was conductee in Loess Plateau dryland of Gansu from 1978 to 2002,to study the yield increase of maize-winter wheat rotation system. The results showed that in the dry, normal and humid year, the crop yield and its increasing tendency of different treatments was coincident, and the sequence was MNP>SNP>NP>M>N>CK in the dry and normal year, and NP>MNP>SNP>M>N>CK in the humid year. the order of yield reduce was N>NP>CK>M>MNP>SNP in the dry year, compared with corresponding treatment in the normal year; and the yield increase was N>CK> NP > M > MNP >SNP in the humid year, compared with corresponding treatment in the dry year. The results also indicated, yield increase with chemical fertilizer treatments, especially N treatment, was affected greatly by rainfall, and the yield of straw combined with N and P treatments (SNP, MNP) were influenced lightly by rainfall. The average contribution rate of NP and M treatments on yield increase accounted for 56.28% and 43.72%, respectively. In the year of dry and normal and humid, contribution of NP treatment on yield increase reached 53.25%, 54.00% and 59.93%, while the M treatment was 46.75% and 46.00% and 40.07%, respectively. The contribution rate of N and P (P_2O_5) on yield reached 19.48%, 34.76%, 49.61% and 80.82%, 65.24%,50.39% in NP treatment, especially in the dry year the rate of P up to 88.4%～145.6%. However, the yield increase of SN treatment, the contribution rate of straw accounted for 31.42% in the humid year, which has no significant difference compared with MNP treatment, and the rate of straw up to 69.97% in normal year and 83.10% in humid year, which was 20.46% and 36.88% higher than that in MNP treatment. the yield increasing effect with sole N treatment was reducing gradually while the effect of SNP and MNP treatment was going up markedly with the lengthening of experimental years.