Abstract: Based on the generalized semi-Markov process simulation method, the 3D time-dependent transport code GSMP3D was developed. It used continuous-energy nuclear and atomic data libraries in ACE format. It is suitable for the transient cases of both stochastic and intense neutron fields. A suite of test problems developed by researchers at LANL and LLNL were used to validate probability of initiation methods. The results obtained from GSMP3D agree well with the results obtained from Mercury and MCNP. Both the initiation probability and the burst waiting time of neutron initiation were predicted by this new code. It shows that it is suitable for neutron initiation problem.