In order to analyze and improve the performance of pulse detonation engines (PDEs), detailed detonation processes deserve much more attention. However, the measurements of characteristic parameters are difficult because the flow field in detonation is unsteady, with high pressure and high temperature. A new device based on the emission-absorption principle is developed specially for measuring pulsed temperature in a PDE plume. Experimental results show that the measured pulsed temperature can diagnose the PDE operation, such as multicycle detonation wave formation, operation frequency, and overfilling process. Effects of PDE configuration, operation frequency, and fuel on PDE plume temperature were investigated experimentally. The plume temperature increases with operation frequency. The PDRE average peak plume temperature is much higher than direct-connected PDEs and air-breathing PDEs. The newly developed plume temperature measurement method is simple, cheap, and easy to operate, which provides a useful tool to diagnose PDE multicycle operation and interaction of external flow field and PDE operation.