Although the reaction kinetics of network formation of polymers has been extensively investigated, the role of entanglement between polymers has not been fully elucidated yet. In this study, we discuss the effect of entanglement via multi-chain slip-spring simulations, in which Rouse chains are dispersed in space and connected by slip-springs that mimic the entanglement. For stoichiometric conditions for the systems containing pre-polymers and cross-linkers, the simulations without slip-springs exhibited reaction kinetics that is consistent with the earlier mean-field theory. Meanwhile, the inclusion of slip-springs in the system retards the reaction in the post-gel stage after the percolation of the system. According to the analysis of the network structure, the reaction in the post-gel stage is dominated by the tethered chains. The entanglement indirectly retards the reaction kinetics through the suppression of tethered chain dynamics.