To enhance coverage and improve transmission rate, multi-satellite cooperative transmission is promising. However, analysis related to its performance is still lacking. Therefore, we consider a multi-satellite joint transmission scenario where the typical user can be served by multiple satellites, and spherical poisson point process is adopted to model low-earth-orbit (LEO) satellites. Then, we derive the expression of coverage probability by using stochastic geometry. The correctness of theoretical derivations is confirmed and the influence of network design parameters is illustrated by extensive simulation. Moreover, the performance improvement brought by multi-satellite cooperation is also highlighted.