In this paper, we propose some physical quantities for characterizing gels. Polymer networks (gels) were investigated by Monte Carlo method using a model of free-radical cross-linked polymerization in a continuous system. The distributions of the degree of polymerization for clusters in this simulation are in good qualitative agreement with experimental results. Linkers can be classified into two types according to their role in the network: One forms a simple closed loop within a polymer, and another forms polymer clusters. Their respective amounts and ratios are examined with regard to changes in the distribution of the degree of polymerization.