As the country's requirements for safe production become more and more stringent, the location selection of offshore oilfield platform sites does not completely depend on economic development benefits. The increase in drilling and completion investment caused by the slip in positioning of drilling platforms and the safety of large-scale facilities have also become indispensable optimizing factors. therefore, in addition to considering the minimum total footage of drilling and completion, it is also necessary to consider the formation soil condition and the number of positioning times of drilling platforms in the later stage. On the basis of the minimum footage and the lowest cost, the platform position distribution boundary is reasonably determined, and the alternative position of the platform is determined by the three-figure method. The calculation model of the slip factor optimization and the optimization method based on the slip factor are established. The application examples in KL10-4 oilfield show that the platform site optimization method based on slip factor can reduce the drilling and completion investment by about 20 million which provides a new method and idea for the site optimization of offshore cluster well development platform.