As one of the most important raw materials for fused deposition modeling (FDM) 3D printing, polyamide (PA) is widely used in many fields because of its excellent properties. For PA FDM, the parameters are highly important to the performance of the printed parts without doubt. Herein, the effect of two main printing parameters (nozzle temperature and layer thickness) on the mechanical properties and tribological properties of FDM-printed PA were investigated. Results show that the mechanical properties of PA increase yet the wear rate reduces with the increase of nozzle temperature from 240 °C to 260 °C, while the friction coefficient (COF) shows few variation. With the increase of layer thickness from 0.1   mm to 0.3   mm, the mechanical properties decline, while the COF increases. Surprisingly, polishing of the 3D printed PA increases the COF to the range of 0.40 to 0.60 from about 0.05 of unpolished, which is attributed to the disappearance of the smooth and hard surface layer caused by extrusion after polishing. For demonstrate, planetary gears were manufactured with the optimized parameters of nozzle temperature of 260 ℃ and layer thickness of 0.1   mm, found running stably at 200   rpm/min without any noise.