A new smart sensor node to monitor soil temperature, including hardware and software, is developed through modular method. The hardware system is developed based on a CC2430 micro-controller and DS18B20. The software system includes the temperature collection and information transmission. The results show that the node can collect soil temperature data and then send the data to the upper network node. This node possesses compact structure, stable performance and low energy consumption. The effective communications distance among nodes reaches 80m and the error ratio is approximately 1%, which meets the requirement of precision agriculture. The node provides a better hardware platform for further study on the communication protocols of wireless sensor networks.