Devising micro-groove structure on the surface of smooth circular pipe can reduce the resistance along the pipeline and then it is able to reduce the energy consumption of pipeline transportation. In order to investigate the influence of the groove size on the drag reduction effect and mechanism, the circular pipe with discontinuous triangular grooves was compared with the ordinary circular pipe, and the Realizable k-ε turbulence model was used for numerical simulation through irrelevance verification. The results show that when the size \(s_{1}^{ + }\) is 9.5, \(s_{2}^{ + }\) is 21.5 and \(h^{ + }\) is 11.5, the grooved circular tube has the best drag reduction effect. The pressure drop is reduced by 22.75% and the friction resistance is reduced by 7.47% at the incoming flow velocity of 2m/s. Comparing and analyzing the velocity, turbulent kinetic energy and other contours in the tube, it is found that the grooved structure increases the thickness of the viscous bottom layer in the boundary layer, so that the groove is filled with low-velocity fluid, verifying the existing theory of bionic drag reduction.