This paper constructs a mental health probability space based on the law of large numbers. First, this paper defines and predicts the transition of personal emotion and the transmission of emotion. This study treats emotion as two random stages. At the same time, according to the initial parameters of each different stage model, a psychological model with individual characteristics based on the Markov chain is established. It can predict the outcome of emotional activities emotionally. Finally, numerical simulation is carried out with Matlab. The results show that the prediction method can well reflect the emotional state transmission. It can be used in psychological prediction simulations of individuals. The mental health statistical model based on the law of large numbers established in this paper opens up a new way for individual psychological counseling and mental health training.