Abstract: To enable the public to monitor the environmental radiation levels independently, an environmental radiation detector was developed based on the principle of direct measurement of X/γ rays by PIN photodiode. The detection system was controlled by intelligent terminal. The weak signal amplifier circuit was designed in the detector module. And the control and communication modules were designed based on the microcontroller (MCU). The environmental radiation detector has the characteristics of low cost, low power consumption, small size, easy to use and easy networking. The characteristics of the system were tested in National Radiation Measurement Station, which are in accordance with the requirements of national standard JJG 521—2006.