A moisture and temperature control system is developed for terminal box in transformer substation. It is composed of wireless temperature and humidity controller, infrared handheld device and monitoring platform. The controller exchanges information with platform by ZigBee wireless network, the handheld device reads and sets parameters in controller via infrared ray. This paper presents a new anti-condensation control scheme and develops a semiconductor refrigeration dehumidifier device. With fuzzy PID technology, it makes a good moistureproof effect by using refrigeration technique to dehumidify. It will be convenient for operators on daily site checking by using handheld device. Operators achieve function of centralized monitoring through platform. This paper discusses the hardware and software design about system, focusing on design of wireless temperature and humidity controller. At present, the system has a high practicability, which has been put into use in some substation.