The effect of reducing chemical fertilizer and replacing with organic fertilizer on increasing water storage in reservoirs and yield of maize in semi-humid and drought-prone areas of Loess Plateau was studied to provide an important theoretical basis for increasing yield and efficiency of maize in dry land，and to solve the contradiction of land use and land conservation through reasonable fertilization.In this study，Jinkeyu 3306 was used as the materia，and the field experiment was carried out by using and a 3-factor 5-level quadratic general rotary combination design from 2018 to 2020. Five chemical fertilizer rates were 395.4，600，900，1200，1404.6 kg·hm-2；five straw returning proportions were 32.95%，50%，75%，100%，117.05%； five organic fertilizer rates were 2385，7500，15000，22500，27615 kg·hm-2. Single application of chemical fertilizer(1200 kg·hm-2)was used as a control.The results showed that the soil bulk density increased with the increasing of chemical fertilizer rates.The application of organic fertilizer and straw returning could both reduce soil bulk density，which is beneficial to soil water storage.With the increase of fertilization rates，the 0～200 cm soil layer water storage increased with the increase of organic fertilizer and straw returning，but the increased 0～200 cm soil layer water storage with straw returning was larger than that of organic fertilizer.Maize yields would be increased by applying chemical fertilizer with organic fertilizer，followed by chemical fertilizer with straw returning.Therefore，the application of organic fertilizer could significantly reduce soil bulk density，increase soil water storage and improve crop yield and water use efficiency.The optimum combination was of chemical fertilizer application 795～1061 kg·hm-2，the proportion of straw returning 69%～ 89%(equivalent to 4399～5674 kg·hm-2)，organic fertilizer application 11723～18848 kg·hm-2，and the expected maize yield was 13232 kg·hm-2.Compared with the chemical fertilizer control(11729 kg·hm-2)，the maize yield of the optimum combination increased by 12.8%，and the chemical fertilizer application decreased by 139～405 kg·hm-2.