Abstract: In this paper,two approaches of FEL spectral measurements are described.One is conducted by using a wave-guide dispersive line and the other by a band-pass filter spectrometer.The dispersive line system consists of a microwave horn,a standard rectangular wave-guide of 150m long,an attenuator,a crystal detector,and a probe to obtain a reference signal.In order to avoid electromagnetic disturbance,the probe is of a dually shielded construction.The bandpass filter spectrometer consists of many directional couplers,band-pass filters,attenuators and a common crystal detector.In fact it is a spectrometer of many channels and the configuration is elaborately designed.The signal of each channel is displayed on a fast oscillocope.Of course,the band-pass spectrometer can be operated with only one channel.In that case,spectral diagnoses are performed by placing different band-pass filters each time and the spectra must be assembled from successive shots.The resolution is determined by the band width of the band-pass filter.And so.good results of the measurments are obtained with many shots and band-filters with narrow band widths.We have performed two FEL experiments on the EPA-74 accelerator.The first experiment is operated in Raman regime using an annular beam (-1kA),which has a 4cm diameter and a thicknees of 1mm and propagates through a drift tube of 5.2cm I.D..28-38GHz radiation frequencies are measured by a wave-guide dispersive line with B1 from 5 to 8kGs.Bw from 0.6 to 0.9kGs.and the electron energy E_e=0.5MeV.The second experiment is performed with a solid electron beam of 5mm diameter (300A).The beam propagates through a drift tube of 1.6 cm I.D..In that case,we have observed radiation frequencies ranging from 25to33GHz.which are obtained by the band-pass filter spectrometer with B1=8kGs.Bw from 0.6 to 1kGs and E_e=0.6MeV.