Abstract: In view of the quick variance of high injection pressure of Chang- 8 oil block in Xifeng oilfield, the reasons of which has been analyzed from the following three aspects: reservoir feature, laboratory testing on injection damage mechanism and the effectiveness of water block remover in the oilfield, thus a kind of FH-01 water block remover has been worked out, of which the pH value is 7 - 8 and it has the characteristics of scaling control, stabilizing formation clay and scale cleanout. With the water block remover in the block where there are 22 water wells under experiment, the results indicate that the broken down effectiveness is obvious, and the average decreased injection pressure is 0. 8 MPa.