For the problem of poor accuracy for catheter axial forming caused by the uncertainty of flaring extension amount during the flaring process of catheter, based on the specific parameters requirements of catheter flaring, the flaring process of LF2M   aluminum alloy catheter with Φ22 mm×1 mm was finite element simulated and analyzed by ABAQUS, and the load-stroke variation law of spinning rod and the contact variation laws between the spinning rod, the flared end of catheter and the flat nozzle were obtained during the forming process. Then, on this basis, the variation laws of end distance-stroke for spinning rod and the maximum outside diameter-stroke for spinning rod under different extension amounts were studied. The results show that the different flared ends formed with the stroke of a specific spinning rod meet the forming parameters requirements under different extension amounts, but the optional range of extension amount is large, which seriously affects the axial forming precision of catheter and requires precise control of extension amount. Based on the variation law of flaring, the reference extension amount is determined, and the corresponding process experiment research is carried out to provide a theoretical basis for the determination of standard extension amount.