Diffraction grating is a very important dispersive element, and it has been commonly used in the field of spectral analysis, the measurement of a diffraction grating’s spectral diffraction efficiencies is essential for evaluating its performance in practical applications and improving its manufacturing technique. In the currently popular measurement technique for obtaining the spectral diffractionefficiencies of a plane grating, because of the hundreds of repetitions of two kinds of time-consuming mechanical movements during the measuring process, the major drawback of this technique is the slow measuring speed, for example, approximately 5-8minutes are needed to obtain the spectral diffraction efficiencies of a broad band pulse compression gratings from 700 to 900 nm (in sampling steps of 1 nm). In our earlier research, we presented a motionless and fast measurement technique for obtaining the spectral diffraction efficiencies of a plane grating, and the new method was based on the employment of an acousto-optical tunable filter, an integrating sphere and a fast data acquisition system, the new methodcan measure the plane grating’s spectral diffraction efficiencies (in the wave range of 700～900 nm) successfullyon a milli second time scale without the involvement of mechanical movements. In this paper, firstly, we analyze the error source of the new measurement method, and we find that the major error source is that the transmittance of the convex lens is a function of the incident angle; then, based on optical simulation, we obtain the relationship of the convex lens’s optical transmittance versus the incident angle, and meanwhile propose the method to correctthe error; finally, based on the experimental result, the error correction method is experimentally tested. Data analysis result demonstrates that, in the wave range of 700～900 nm, the mean absolute error between the two measured spectral diffraction efficiencies by using the new and the currently popular methods has been decreased from 0.207% (before error correction) to 0.099% (after error correction), considering the measurement accuracyof the currently popular method is around 0.1%, we think the error correction method provided in this paper can successfully eliminate the main error source of the new measurement technique for obtaining the spectral diffraction efficiencies of a grating.