In order to investigate the transient response characteristics of photovoltaic detectors irradiated by short-pulse laser, the response waveforms of a HgCdTe photodiode to laser pulses with 16 ns duration and different laser intensities were measured. The photodiode worked with room temperature and zero bias, and the laser wavelength was in the response spectrum of the photodiode. In the detector′s linearly logarithmic response zone, the signal waveform broadened gradually with the incident laser energy density from 7.2 nJ/cm2 to 75 μJ/cm2. The full width at half maximum of signal waveform rose to 235 ns from 55 ns, at the same time the bottom width rose to 380 ns from 170 ns. The pulse response broadening of the detector implied degradation of its transient response characteristics. The mechanism of the response degradation was explained via analysis on the diffusion process of photocarriers in the quasineutral region and on the changes of junction electric field and junction capacitance under high-injection condition.