With programmable power output capabilities, global positioning system(GPS) Block IIR-M and Block IIF satellites can flexibly enhance transmit power of individual signal components. In order to systematically evaluate the power enhancement capability of GPS P(Y) codes, the theoretical analysis of the flex power principle was conducted, and a monitoring and analysis method of GPS signal power enhancement was proposed. Furthermore, the coverage, constellation performance, signal-in-space and user-side performance of power-enhanced P(Y) codes were analyzed based on the data of the International GNSS monitoring and assessment system (iGMAS) and international GNSS service (IGS) monitoring station, high-gain antenna monitoring data, and precision ephemeris. According to the findings, it is possible to increase the L1 P(Y) code and L2 P(Y) code power of Block IIF and Block IIR-M satellites by about 6 dB and 5 dB, respectively, compared with the normal level, while keeping the total transmit power and civil signal power unchanged. With respect to the dual-frequency single-point positioning test only using 19 enhanced satellites, the positioning accuracy is no more than 15 m (95%) in the power-enhanced signal coverage area. While the equivalent carrier-to-noise ratio reduction caused by multi-access interference between P(Y) codes is 0.4 dB, when there are 6 visible enhanced satellites and the enhanced P(Y) code carrier-to-noise ratio is 55 dB·Hz.