In order to monitor the dynamic change of gas production from coal reservoir, especially the dynamic change at the initial stage of gas production of coal reservoir, a visual and pressure-resistant simulation device for the CBM well annulus was built, A needle type of monitoring device based on the difference of conductivity between gas and liquid is made, and testing the reliability of the monitoring device under high solid loading and strong disturbance condition, stimulating gas–liquid two-phase flow in the annulus under 0.8 MPa and gas production from 0 to 150 m3/10 min. The results of the simulated and monitoring show that: In the process of increasing the volume of gas, the size, distribution, shape, trajectory, and speed of bubbles is always changing. Analyzing of the fluid flow characteristics through slow camera picturing and monitoring curve, the entire process is divided into six fluid flow characteristic intervals, and the characteristic curve corresponding to the fluid flow characteristic interval is identified. Through the corresponding characteristic curves, the change of gas production from coal reservoirs can be quickly and qualitatively determined, which provides a new technical means for production monitoring of CBM wells.