Linear power supply is widely used as the driving power of semiconductor laser because of its advantages such as low interference and fast dynamic response. To solve the problem that the regulating tube fails due to excessive power consumption, this paper proposes a hybrid pulse width-pulse amplitude modulation strategy, which uses the drain-source voltage and drain-current of the regulating tube to modulate high frequency square wave, and calculate the mean value of square wave, based on which the regulating tube power consumption detection circuit is designed. An experimental platform is built to test the circuit, and the results show that the circuit has the advantages of excellent detection accuracy, low hardware cost and fast response. The circuit has a maximum relative error of $- 2.64{\text{%}} $ and a linearity fit of $ 0.9987 $. It can be widely used for power consumption measurement and safety zone protection of regulating tube.