A polymer microfluidic chip which was actually used for droplet generation and ddPCR detection was taken as the research object. According to the specific structural characteristics of its microchannel, the relationship between the droplet generation size and the theory driving pressure required by the continuous phase (fluorine oil) and discrete phase (deionized water) was studied. Through the designed experimental testing equipment platform and the computer image processing method, the droplets generated under the driving pressure range were subjected to image shooting, size measurement and uniformity analysis. The results show that the driving pressure of continuous phase (fluorine oil) and discrete phase (deionized water) are 31 kPa and 26 kPa respectively, which can stably produce droplets that meet the requirements of size index, with good spherical shape and obvious droplet boundary; the results of image measurement and detection processing are close to the average value of the sampling of the software matched with the CCD high-speed camera, and the error is controlled within 2 μm, which can realize rapid detection, convenient application and strong operability.