A novel MEMS microwave power coupler based on GaAs for Ku-band(12.4～18 Ghz) is presented to improve the existing technology for measuring microwave power based on the termination devices, such as thermistors, thermocouples, and diodes,because the signals are not available after power detection by these devices. By the designed coupler, the microwave power is coupled with the Coplanar Waveguide(CPW)line, and most of the CPW signals can be transmitted to the next stage circuit for further processing. In order to reduce the reflection losses and to obtain broadband response of the power sensor, two kinds of optimal methods with a tuned structure and a compensating capacitor are proposed. Optimizations of the design with HFSS has demonstrated that the return loss(S₁₁) and insertion loss (S_{21) at the central frequency of 15.2 GHz have reached -42.90 dB and -0.15 dB, respectively and the deviation of S11 and S21 compared with the central frequency have reached ±6.41 dB and ±0.04 dB in the Ku-band.These results show the microwave power coupler has advantages of dB and ±0.04 dB in the Ku-band.These results show the microwave power coupler has advantages of high isolation, low loss and broadband characteristics.}