The metal resonant cavity method working with TE_01δ mode is a universal method for evaluating the microwave dielectric properties of low-loss materials. All the microwave dielectric resonators are multi-mode resonators, so the correct identification of TE_01δ mode is the basis for the microwave dielectric measurements. The TE_01δ mode can be identified by predicting the resonant frequency and its variation with resonator size, expelling the spurious modes according to the exciting conditions, etc., while these methods are relatively complex and sometimes unreliable. In the present work, a simple method for accurately identifying the TE_01δ mode is developed. A low-loss reference sample with known dielectric properties is introduced and placed in the cavity for the first step, and the to-be-measured sample is placed on the reference sample for the second step. The rough permittivity of the to-be-measured sample can be calculated from the TE_01δ-mode resonant frequencies in the two steps through the finite element analysis, and is used to predict the resonant frequency for TE_01δ mode when only the to-be-measured sample is placed in the cavity. The difference between the predicted and measured TE_01δ-mode resonant frequencies for the to-be-measured sample is less than 1%, so that the TE_01δ mode can be easily distinguished from the spurious modes and accurately identified.