This paper proposes a perfect electromagnetic absorber composed of a trapezoidal silver metal-dielectric array and a double-layer base layer. Based on the finite element method, the absorber achieves an absorption efficiency in the near-infrared band of 99.91% under transverse-electric (TE) polarization, and 93.40% under transverse-magnetic (TM) polarization. And the accuracy of this calculation result is verified by the finite difference time domain method. By analyzing the distribution of electric field intensity under other parameters, the mechanism of the structure parameters to affect the absorption efficiency is studied. Finally, the manufacturing tolerance of each structural parameter is calculated when the absorption efficiency is above 90%. Trapezoidal perfect narrow-band absorber can be applied in optical sensor and optical detection.