Abstract: Using micro-fluidic particle image velocimetry(micro—PIV)technique, the paper investigated measurements for the square micro—channel with side lengths of 800pm. To attain distinct particle image, solve the problems of matching camera with PIV system and improve the image'S signal—to-noise ratio, the research adopted 10x microscope, 14一bit CCD camera system, 3μm fluorescent particles and filter lens that only allow 610nm red light penetration. In the image processing, Brownian motion'S impact on tracing particles was eliminated by the average of images. Using ensemble correlation arithmetic acquired velocity distribution and velocity streamline. The results show that iags'flow structure iS basically consistent inside the micro-channel. The fully developed internal flow in the channel is a cycling movement. There exists low speed vortex area in the micro-channel'S flat top and corner. whose vortex structure and size depend on time and Reynolds number. The particles are vulnerable to deposit in the low—speed vortex area, which proves the main factor for block.