In this paper, the abnormal optical absorption of subwavelength trapezoidal metal groove arrays illuminated by a plane wave was systematically studied by the rigorous coupled wave analysis method. The influences of structural parameters on the absorption efficiency of sub-wavelength metal trapezoidal groove arrays were simulated, and a semi-analytical Fabry-Perot model was introduced to analyze the calculation results. The results show that the absorption enhancement of the sub-wavelength metal trapezoidal groove arrays is mainly caused by the Fabry-Perot resonance effect of the in-groove mode and energy conduction coupling of surface plasmons between the arrays. The absorption peak value of the metal trapezoidal groove approaches 1 when the groove depth satisfies the Fabry-Perot resonance condition and the array period satisfies the surface plasmon excitation condition. By compared with the rectangular groove, the trapezoidal groove with an appropriate inclination angle can not only ensure the absorptivity but also relax the tolerance of the groove depth, which helps in reducing the difficulty of device processing and improves the feasibility of device design.