In order to monitor the aquatic environment and fish state in offshore aquaculture cage farm daily, a centralized remote monitoring system for bred fish was developed. The system was composed of remote detecting node (RDN) and local monitor and control center (LMCC). RDN based on the techniques of multi-beam detection and multi-path signal process was placed in the center of a cage to scan the inner cage and measure the aquatic environment. LMCC based on LabVIEW was placed in the office to manage all the remote detecting nodes remotely and show fish state. The communication between LMCC and RDN depended on GPRS wireless data transmission technology. The system prototype was tested in the field of offshore aquaculture cage farm in Quanzhou, Fujian province. The results show that the system is reasonable design, simple operation, easy placement, and robust under different environmental conditions. It can real-time monitor the aquatic environment and fish activity remotely, provide users with a variety of information such as fish amount, fish growth in the offshore fish cage, and give an alarm in the time when net clothing damage or fish escape.