Abstract: This study focused on black soil of Lalin open-air vegetable fields in Heilongjiang Province and analyzed the effect on soil phosphorus transformation under the following treatment,conventional irrigation and fertilization（WF）,reducing fertilization treatment（W80%F）,reducing irrigation treatment（80%WF）,and reducing irrigation and fertilization combined with straw return treatment（80%W80%F+S）.The results showed that the vertical variation characteristics of total phosphorus and available phosphorus in all treatments were obvious,which decreased with increasing soil depth,and the total phosphorus and available phosphorus content in 0-20 cm soil layer was higher than those in other soil layers,reducing irrigation and fertilization combined with straw return treatment significantly reduced the available phosphorus contents in deeper soil（P＜0.05）by 57.0%,thus inhibiting phosphorus moving to deeper layers.With the extending of cabbage growth stages,the available phosphorus contents in soil of reducing fertilization and conventional water and fertilizer treatments increased continually;the available phosphorus content in soils of reducing irrigation,reducing irrigation and fertilization combined with straw return treatments continued decreased continually.Available phosphorus contents decreased slowly after reaching the highest level in the middle and late stages of cabbage growth.Reducing irrigation and fertilization combined with straw return treatment could reduce the risk of soil phosphorus leaching and reduce the total phosphorus content in the leaching solution,which was a feasible irrigation and fertilization scheme with the lowest risk to the environment.