Abstract: Energy variation in pulsed electron beam could result in corkscrew motion of the beam centroid in linear induction accelerator, therefore enlarge and distort the spot size of the accelerator. The method using Cerenkov radiation produced by the electrons passing through the quartz to measure the time resolved energy spectrum is described in this paper. The time resolved energy spectrum diagnostics has been carried out for the pulsed intense electron beam of 2MeV injector at Institute of Fluid Physics of CAEP. Comparison of the experimental results between time resolved energy spectra and diode voltage waveforms are given and analysed. The measured energy is about 2.2MeV， the maximum energy variation in 60ns is 4%。