Based on the loss parameters of silicon waveguide, waveguide crossing and microresonator based optical switching elements, a general analytical model to study the transmission loss in Torus-based optical network on chip (ONoC) was proposed. The model was used to analyze insertion loss at device level, router level and network level. Meanwhile, the automatic analysis system was established. The maximal insertion loss in different network scales was obtained from the analysis system. The maximal insertion loss of the Torus-based ONoC using the Crossbar, Cygnus and Crux was also analyzed. From the numerical investigation, it can be obtained that the insertion loss enlarges with the increasing network scale and the minimum insertion loss is presented at condition of M=N. Meanwhile, compared with the Crossbar and Cygnus, the insertion loss of the ONoC using Crux is minimum. The insertion loss of the ONoC using Crux is less than the insertion loss of the ONoC using Cygnus about 5 dB.