The operating principle of optical fiber F P temperature sensor is analyzed aiming at the problem that temperature is difficulty of the real time measurement in the study of thermal interaction between laser and bio tissue. The temperature sensing model of F P cavity is discussed. The low fineness optical fiber F P sensing system for temperature measurement is designed and set up. The real time temperature field measurement system of the bio tissue irradiated by pulse laser is built based on the sensing system. The temperature distribution generated by laser in the different place apart from the bio tissue coat is studied through experiment. The experimental results show that the sensing system can be used for the real time temperature measurement of bio tissue efficiency. The system has small size and its outer diameter is only 250 μm. And the hurt for bio tissue is small. It has high respond speed and the respond time of temperature is less than 1s. These can be satisfied with practice demand. The detected ascending temperature of bio tissue decreases with increasing distance between sensor and laser, and the respond time of sensing system is long.