Common software synchronous sampling methods have some shortcomings such as sampling synchronization error, sampling interval error accumulation increment and so on, and the impact of this error on the measurement accuracy can not be ignored [1]. In this paper, analysis on synchronization error occurrence reasons was performed, and proposed the synchronization implementation method of asynchronous sampling. This method can track the real-time changes of electrical signal by the zero-cross-over triggering circuit, and reduce the synchronization error by the software method. Simulation analysis of the signal cycle (frequency) and RMS measurement shows that proposed method improves accuracy of the electrical signal parameters measurement based on microprocessor technology.