The interconversion and coupling of multiple energy sources in integrated energy systems (IES) lead to highly complex and variable operating states. Therefore, it is essential to establish a model capable of accurately describing the operating states and transition logic of IES, providing precise references for optimal scheduling. However, traditional IES modeling methods primarily focus on input-output relationships, which makes it difficult to clearly describe the operating states and state transition process in different stages. To address this issue, this paper proposes a state transition modeling method for IES based on hybrid automatic (HA). First, the operating states of the IES and their transition conditions are described in detail, and a state transition model of the IES is established based on HA. Second, a method to determine the initial state transition path of the IES is developed with the objective of minimizing the daily operation cost of the IES. Finally, a method to solve the day-ahead optimal state transition path of the IES is proposed through cost analysis of the state transition model. Numerical simulations show that compared with traditional modeling methods, the proposed method not only ensures the optimality of the solution but also significantly reduces computation time. Moreover, it mitigates fluctuations in equipment output and interconnection line power under rapid renewable energy variations, thereby enhancing equipment reliability and overall system stability.