In order to improve the efficiency of water utilization in mountain orchards, an automatic irrigation control system based on soil moisture was designed. The system was composed of an S3C2440 ZigBee gateway, several CC2530 soil moisture sensing nodes and irrigation controlling nodes. In addition, solar batteries were applied to provide extra power and recharge lithium batteries. Using the self organized ZigBee network, the gateway collected and updated soil moisture data to internet server for decision support. Therefore, irrigation process was handled according to soil moisture. The system test in a mountain orchard showed that the wireless network had a low packet loss rate(less than 15%), and maintained soil moisture in a suitable range (above 18%) for plant growth.