In order to realize the multi-color 3D model rapid prototyping effect about FDM (fused deposition molding) 3D printing technology, a multi-nozzle 3D printer based on three sets of nozzles was designed,which could print interference-free.Through analyzing the single-head 3D printer workflow, it was compared the characteristics of multi-nozzle 3D printer were more nozzle and complex linkage. So, the key technologies of the multi-nozzle 3D printer were the nozzle preheating time and the nozzle switching accuracy. The control flow was analyzed and control system was researched. Finally, the preheating time of multiple nozzles was calculated according to the linear conversion method, and the coordinate switching precision of multiple nozzles was compensated according to three-dimensional space correction method.