A newly designed grating used in terahertz region is proposed,which is composed of the trapezoidal elements repeated successively along one dimension of the substrate,and uniform interval (the grating period) repeated along the other dimension.The transmission of the grating owns a designable trapezoidal profile dependent on the geometric dimensions of the element.The far-field diffraction pattes of a designed grating at incident broadband terahertz frequencies,with element dimensions of upper,lower side and period of 50,250,and 300 μm,respectively,are simulated by the scalar diffraction theory.The simulation results indicate that the terahertz grating exhibits a property of single-order diffraction,and the diffraction efficiency of the first order reaches 6.6％,exceeding that of a traditional sinusoidal amplitude grating with identical period and duty cycle.Owing to the regular architecture and the high single-order diffraction efficiency,the grating is easy to fabricate and shows great potential applications in single-shot spectral measurements of weak broadband terahertz pulse.