The present invention provides a power measurement apparatus and method for a pulsed terahertz quantum-cascade laser (THz QCL). The apparatus includes a light source part, a light path part, and a detection part. Terahertz light emitted by a THz QCL reaches a terahertz quantum-well photodetector (THz QWP) through the measurement apparatus, and is absorbed to generate a corresponding current signal. A signal processing circuit extracts a voltage signal from the current signal, amplifies the voltage signal, and inputs the amplified voltage signal to an oscilloscope for reading and displaying. According to a responsivity of the THz QWP at a lasing frequency of the laser, the measurement of the output power of the pulsed THz QCL is acquired. The present invention avoids integration estimation when a thermal detector is used to measure output power of a THz QCL in a pulse operating mode, and can directly acquire the power value of a pulsed output from the laser according to the amplitude of the detector responding to the pulsed terahertz light.