In order to solve the problem of higher relief capacity of trapped-oil in high speed gear pumps, a new relief groove and its geometric dimension with straight U-shaped cross section and flat end surface is proposed. Its relief area and its followed trapped-oil pressure were emulated and compared to relative results of common rectangular-shaped relief groove. All results show that the maximum relief area of U-shaped relief groove is increased by 13.5%, the shortage relief capacity near the minimum trapped-oil volume is preferably solved, and its processing is simple and 〖JP+1〗easy; the increased percent of trapped-oil pressure peak value is only 15.9% in 8 000 r/min high revolving speed, and the minimum trapped-oil pressure is -0.26 MPa, which can be regarded as relatively mild trapped-oil phenomenon; but the 25.1% and -0.61 MPa in rectangular-shaped relief groove is regarded as relatively serious trapped-oil phenomenon.