The utility model relates to a power detection circuit which comprises a pi attenuator circuit, an input matching circuit and a power detection circuit, wherein the pi attenuator circuit comprises a resistor R1, a resistor R2, and a resistor R3, attenuates radio frequency incoming signals RF-IN and adjusts the signals into the detection scope of the power detection circuit, The input matching circuit comprises capacitors C4 and C5, an inductor L1 and a resistor R4, is designed according to the frequency of the radio frequency incoming signals, and outputs matched radiofrequency signals to the power detection circuit, and the power detection circuit detects the power of the radio frequency incoming signals, and Vout outputs corresponding level signals. For radio frequency communication system within an ultrashort wave and decimeter wave frequency scope, certain signal level can be output by detecting the power of the radiofrequency signals to indicate the power change of mean square deviation power of carrier waves. The circuit is simple, reliable and flexible and can be applied to lots of cases.