Abstract: In order to study the change law of reliability over time in the process of coal seam water injection, multilevel flow models were used to establish the model of coal seam water injection system and describe the relationship between the target and the function. By using the concept of time points and the failure over time, which was in the system reliability analysis method based on the multilevel flow models, the process of coal seam water injection was divided into several periods, and the interval was set to four hours, then the reliability of the system and the subsystem was calculated at all-time points. The polynomial fitting and exponential fitting was used to analyze the error, the polynomial fitting effect was better, and the system reliability was predicted by fitting curve equation. The results showed that in the process of coal seam water injection, the system reliability changed in accordance with the four polynomial rule of time under the influence of failure parts. Based on multilevel flow models, the system reliability analysis method could express system knowledge on different abstract levels, it was useful to find the weakness of system, and it had high application value for the system prediction and the equipment maintenance management.