Basing on pyroclectric theory, a novel millimeter wave ther enetgy detectot with high sensitivity and fast response has been proposed and designed. We calibrated it at different operating frequencies separately. Its main propetty Parameters have been given. Sensitivity of this energy meter is about several ten mV/μJ, which is four to five orders higher thsn traditional detector. Its time response is less than 1 μs. The speed of response has been improved by six to seven orders. This energy meter has been used in detective system of Raman free-electron laser. We successfully measured the typical parameters of the output millimeter wave laser pulse.