A Monte Carlo simulation algorithm for investigating the structural growth in a polymer-polyfunctional monomer system and the method to obtain the required simulation parameters are proposed. Combining the Monte Carlo sampling technique and swell ratio experiments, the molecular structural evolution in crosslinking LDPE-TMPTMA systems is explored. The crosslinking level can be effectively promoted at high TMPTMA concentrations and at high cure temperatures. With increasing overall crosslinking density, gelation occurs at lower degree of conversions; the gel crosslinking density increases; the TMPTMA densities in both sol and gel fractions also increase; while the sol polymer molecular weights and the sol crosslinking density decrease. The implications of the simulated results to the processing of LDPE-TMPTMA compounds are also discussed.