This paper briefly presents the working principle of micro-PIV (Particle Imaging Velocimetry) and its development and application on the microscale flow. Compared with ordinary PIV, micro-PIV has much higher spatial resolution. In addition, the adoption of fluorescent tracer and filter lens could enable flow field near wall surface to be measured. In view of the ordinary 2-D PIVs have been widespread among the scientific research institution related on fluid flow, the way that an ordinary 2-D PIV was modified to enable measurement of microscale flow was discussed in the paper. The extra elements of microscope objective lens, relay mirror, filter lens and telescopic focusing barrel are necessary. Some experiment results of the flow in microscale channels have been introduced to verify the availability of the modified PIV system. It could be found from the experimental results that the modified PIV system could be feasible and reliable for measuring micro-scale flows.