In order to solve the problem of high transmission latency in the current data processing mode of Spatial Information Network (SIN), a low latency on-orbit collaborative computing strategy based on computation dependent routing is proposed. Considering the dynamic change of satellite network and the heterogeneity of satellite computing resources, an element time expanded graph model is proposed to realize the computing resources of satellite and shield the SIN dynamic characteristic. On this basis, a mathematical model of multi-satellite on-orbit collaborative computing based on computation dependent routing is constructed, and the latency optimization problem is proposed. To solve the above problem, an improved Hetergenetous Earliest Finish Time (HEFT) algorithm is designed. The simulation results show that the on-orbit collaborative computation can effectively reduce the task processing latency of satellite date, and the proposed improved HEFT algorithm reduce the task processing latency substantially with a little and acceptable convergence performance.