In order to reduce the safety risk in the construction of cross power transmission line, an intelligent monitoring system is designed to monitor various state parameters of crossing frame and to early warn the possible crises. In this system, the monitored data is transmitted to the ground mobile monitoring equipment to process and display through wireless communication mode, and the WiFi and wireless relay technology are used to expand the coverage of wireless signal. And data acquisition and wireless transmission process together with and the structure of data processing software for the mobile monitoring device are expounded. Field experiments show that changes in the state of the cross frame can be monitored accurately by the system.