Rotary steerable drilling tool works in harsh environment underground. The communication system in tools need the following characteristics,such as high temperature resistance, high reliability, realtime capability and flexible expansion capability. This paper describes the design of CAN bus communication system based on HI3110 chip,introduces CAN bus communication nodes hardware structure and software work flow with HI3110 and MCU.Laboratory tests show that the communication bit error rate can reach 10-5in ambient temperature 125 ℃. The communication system meets requirements of rotary steerable tool with high temperature resistance, high reliability and realtime capability, and obtained the good effect in engineering application of rotary steerable drilling tool.