Glass fibre (GF) and glass bead (GB)–reinforced polyamide1212 (PA1212) was additively manufactured by selective laser sintering. The effects of laser power and GF content on the tensile and tribological properties of the printed specimens with a base GB weight fraction of 40 wt.% were investigated. The strengthening mechanism of GFs/GBs was illustrated by analyzing the interfacial adhesion between the fillers and the PA1212 matrix. The specimens with 40 wt.% GBs and 10 wt.% GFs fabricated at a laser power of 30 W exhibited a strength of 52 MPa, a friction coefficient of 0.23, and a wear rate of 0.0011 mm3/N·m. The selected optimal laser power and GF addition contributed to the strong interfacial adhesion, which realised flat surface morphology and an adequate encapsulation of fillers in the specimen. The reinforcement of GBs/GFs in PA1212 can serve as a reference for a deeper understanding of the strengthening mechanisms for other additively manufactured engineering plastics.