Abstract: A novel non-contact pressure measurement system of pressure sensitive paint (PSP) was established. One set of test section of millimeter level plane cascade which can be dis-assembled was designed. The surface pressure of blade suction side with and without tip clearance was measured using PSP technology for the first time. The results show that, because of tip clearance, the blade pressure side gas leaks into the suction side through tip clearance and the surface pressure of the top of blade suction side is bigger than it of the bottom. Contrast with the condition of no tip clearance, leakage has significant impact on the pressure on one third of the blade span of suction side, but little on the bottom of suction side.