The nozzle structure characteristics of traditional desktop fused deposition molding (FDM) 3D printer were analyzed,and the nozzle diameter,shrinkage angle and nozzle temperature were selected as experimental variables to carry out orthogonal simulation experiments.The distribution states of the nozzle melt pressure field,velocity field,viscosity field,temperature field and shear rate field were analyzed.To stabilize the exit velocity,the stable outlet section speed,lower melt viscosity and higher outlet pressure were used as optimization goal to improve nozzle printing accuracy and ensure smooth printing process.Through range analysis,the change rules of each optimization index under three factors were determined,and the multi-objective optimization problem was solved based on the genetic algorithm.The results show that the most significant factor affecting the outlet velocity variance is the channel diameter,and the most significant factor affecting the channel melt viscosity and the outlet pressure is the nozzle temperature;considering comprehensively,by using the nozzle with 1 mm diameter and 30° contraction angle and working at 200~210 ℃,the better index of polypropylene melt printing can be achieved.