Abstract: Aimed to the limitations of low porosity and permeability of standstone formations, which had the characters of water blocking damages in development, after core flow tests were conducted to simulate the process of water blocking in laboratory, this paper established a new method to evaluate water blocking damage mechanisms of low permeability sandstone formations. The results shows the oil phase permeability of low permeability sandstone cores will be damaged badly because of the invasion aqueous filtrate of workover fluids, the rate decreases from 7% to 60%, and flow pressure will increase from 1 to 3 times. Based on the results, a method avoiding or removing water blocking is worked out. Laboratory test by the core samples has showed that the chemical system has the giant effects on removing water blocking, which can remove 85% of water blocking. This water blocking remove technique has been applied successfully in different oilfields.