Gas release caused by drainage pipeline failure or abnormal gas effuse at mining area really threatens coalmine safety. The currently-used coalmine gas monitoring and control techniques have difficulty in effectively obtaining real-time gas concentration distribution and estimating gas emission rate in case of coalmine gas release accident. In this paper, a numerical model based on advection-diffusion equation combined with Ensemble Kalman Filter (EnKF) was proposed to estimate coalmine gas release and dispersion. The proposed model was validated by twin experiment, and the sensitivity analysis of first-guess gas release rate is conducted to further demonstrate the feasibility of the proposed model. The reasonable results indicate that the integration of advection-diffusion simulation and EnKF technique is an effective tool for predicting real-time methane concentration distribution and estimating gas emission rate in case of coalmine gas release accident, and also for optimizing the layout and number of methane detectors in coalmine roadway. This study could be helpful for providing technical supports for emergency response and loss prevention in case of coalmine gas release incident.