To effectively describe stochastic deteriorations and environment effects on a system deterioration process, a two-stage deterioration model was proposed for a two-stage deteriorating system. Deterioration pit was used to denote a deterioration region where is going to suffer a deterioration process. The deterioration process is divided into two stages:the deterioration pit initiation process and the deterioration pit growth process. A non-stationary Gamma process and a non-homogeneous Poison process were introduced to model the deterioration pit initiation process and the deterioration pit growth process respectively. By regarding environment changes as random changes and introducing environment effect factor, a two-stage deterioration model with random changes was developed. Based on the deterioration model, a condition-based maintenance model was presented finally. The optimal inspection intervals of the system can be found by minimizing the expected maintenance cost under single stage deterioration model and two-stage deterioration model as different environment effect factors. Finally simulation experiments were designed. Results show that the proposed model is valid and practical for stochastic deterioration systems of decision-making maintenance actions.