The Euler multiphase flow and population equilibrium model were used to simulate the three-phase flow field in the bubble expansion stage of the outlet curved pipe section. The influence of the ratio of the bending diameter and the volume fraction of the gas phase on the pressure loss is revealed, and the safety range of the optimum bending diameter ratio and the volume fraction of the outlet gas phase is determined. The results show that the three-phase flow in the tube is more uniformly distributed in the vertical stage, and when the pipe is curved, the liquid-phase close to the pipe wall gathers along the pipe flank to the outside of the pipe, the solid phase is transferred along the pipe flank to the inside of the pipe, and the gas phase shrinks along the pipe flank to the inner centre. The maximum speed of each phase of the three-phase flow in the elbow is at the wall of the tube from 45° to 60° inside the elbow, and the distribution law along the axial direction of the pipe is about the same as the distribution law of volume fraction. The pressure loss of the elbow decreases with the increase of the bend diameter ratio, when the bend diameter ratio increases to 6, the pressure loss of the pipe decreases sharply, and the pressure loss decreases slowly with the increase of the bend diameter ratio. When the gas phase volume score in the elbow reaches 70%, there will be an obvious wall separation phenomenon, to keep the system in a stable working state and prevent blowout, the gas phase volume score should be controlled within 60%.