The kinematic modeling of 2P-R linkage, which is part of the differential feed mechanism of overlock machine, is built with the method of successive approximation of link length. The mechanism is analyzed with the secant method. The locus curves of center point of feed mechanism, motion curves of execution component are obtained. The performance improvement of the differential feed-dog mechanism is put forward, based on the analysis of variation behavior of feed-dog path. This has great significance for designing overlock machine and improving the working function.