After analyzing the power control mechanisms in wireless sensor networks, the design principles and the classification standards are presented in this paper. Then the fundamental mechanism of the existing representative power control protocols are analyzed in detail, and their classifications, characteristics and performance are compared adequately. Finally, by including the status of current development, the restrictions to the practical applications of wireless sensor networks are summarized, and the importance of establishing an adaptive power control model based on the empirical studies and data analysis method are proposed.