The utility model discloses a separation of impurities device for oil storage tank belongs to oil storage tank field, fusiform separator including vertical setting, divide the matter district that attaches most importance to, mesoplasm district and light district from top to bottom at the separator, having set up heavy matter export in heavy matter district, having set up the light export in the light district, set up separate outlet and separation import respectively in mesoplasm relative both sides in district, the district is provided with buffer at the mesoplasm, and this buffer includes the buffering strip of bumper bracket and a plurality of flexibilities, the equal vertical setting of buffering strip is fixed in the separator and through the bumper bracket. Slow down fast to impurity in the separator, can be at the regional vortex that forms of buffering strip, the vortex that does not exist together also bumps easily, and the different impurity of weight is realized separating down in the centrifugal force effect in the vortex, and does its separation of impurities compare and has improved 3 in its separating rate under the action of gravity 5 doubly. The design of this spindle formula can reduce floor area, can be favorable to the discharge of the impurity of after -separating.