A squall line system causing gale and short-term heavy rainfall during 4-5 July, 2013 was numerically simulated to analyze the effects of latent heating and surface heat fluxes on mesoscale convective system. Results reveal that:(1) Latent heat releasing plays an important role in squall line's development, movement and vertical structure at mature stage. (2) At mature stage,the heating effect on the middle and high level atmosphere by condensation latent heating within cumulus convection intensifies the low-level convergence and high-level divergence, and then the powerful updraft flow in convective system results in stronger latent heating. (3) Condensation latent heating significantly contributes to the low-level inflow and high-level outflow of squall line system. Indirect vertical circulation leads to the enhancement of spreading downward of high-level momentum. (4) The cold downdraft is strengthened by condensation latent heating, which enhances the gust front, and makes new convective cells trigger in front of the squall line system. This system keeps moving forward with dissipation of old cells and continuous generation of new cells. (5) While the vertical coupling structure of high-level and low-level jets promotes the development of squall line, the stronger condensation heating effect of system at mature stage provides a feedback effect on enhancing this vertical coupling to a certain extent. (6) By affecting the antecedent environmental circulation, the surface heating fluxes also play important roles in triggering and maintaining squall line. Firstly, the surface heat flux in the daytime enhances the convective boundary layer turbulent mixing, which gradually develops an unstable stratification that maintains until midnight. Secondly, the boundary layer humidification effect related with surface latent heating flux stores abundant vapor and unstable energy for system's outburst.