Abstract: According to the current problem that bubble detection device commonly used in CBM well cannot meet the requirements for real-time detection ,a down hole real-time detection device for CBM bubble is designed based on optical probe to solve this problem. The core processing component of this device is microprocessor STM32. As the refractive index of light in the air and liquor are different , this device can generate high level or low level signals representing different mediums , then calculate relevant parameters of gas bubble from CBM. This device overcomes shortcomings of conventional bubble detection devices. In terms of both target pertinence and speed of detection ,it meets requirements of real-time detection of gas bubbles in CBM wells ，and can be used to fully understand characterstics of fluid parameters variation and gas- -liquid two- -phase in reservoir and wellbore. The simulation test results of detection device show that detection device has fast response speed and high calculation accuracy , and can meet the engineering requirements of actual project.