In this paper, a new and efficient method is proposed by using wireless sensor networks in on-line monitoring of large electrical equipment to solve the problems of existing on-line monitoring system that wiring too complicated, causing fault diagnosing, maintaining difficulty and so on. The features are described range from CC2431 system-on-chip to TinyOS which is a wireless sensor networks operating system, and nesC which is programming language of TinyOS. The hardware design for wireless sensor network node and base station based on the CC2431 chip and the program design of transplanting TinyOS into the sensorspsila nodes and base stations are discussed in detail. Finally a data multi-hop system is achieved.