In this paper, the method to linearize the non-linearity of diode and to compensate the characteristics change of diode with the temperature is studied. Square root circuit is used to linearize the non-linearity of diode about the input power, and two identical diodes and OP-Amps, which have variable reference, are used to compensate the characteristic change of diode with the temperature. As the result, designed diode power detector (with the square root circuit and temperature compensation circuit) can detect the output power linearly with the 0.23 $pm$0.025V/dBm rate in the case the input power is greater than -6 dBm, and the designed circuit operates stably with no variation in the output data about the temperature change from the room temperature to 8$0^{circ}C$.