The air-to-ground data transmission system developed jointly by the Shaanxi Weather Modification Center and the Xi'an Jingbo Company is described. This system was used in 25 operation flights of rain enhancement in 2002 and 2003, which adopts the transmission mode with wire and wireless combined and can avoid unstable signals in short-wave communication and transmit sound and data normally. With this system, the commanding staff on the ground can learn about the status of the seeding airplane promptly. The real time data of temperature, humidity, flight altitude and flight track from the seeding airplane were compared with the data received on the ground by the Xi'an Weather Modification Center on 19 September 2003. The comparison suggests that the data received in airplane is well in agreement with the transmitted data from the airplane at the same time, and that the system performed well and steadily.