Long glass fiber reinforced polyamide 66 (PA66/LGF) composites are widely used in automobile and other industries due to their excellent comprehensive performance. In this paper, the PA66/LGF composites were prepared by a custom?made melt impregnation equipment, and the mechanical properties, interfacial adhesion and other properties of PA66/LGF composites were characterized. The effects of a series of influence, such as the glass fiber content, lubricant content, compatibilizer content, and pellet length, on the comprehensive properties of composites were investigated. Finally, we summarized the optimal formula design and pellet length for the preparation of PA66/LGF composites. The tensile strength, the elongation at break, the flexural strength, the notched impact strength and the non?notched impact strength of the PA66/LGF composites with a glass fiber content of 43 % and a pellet length of 12 mm prepared in this study were 230 MPa, 7.1 %,369 MPa,62 kJ/m2,90 kJ/m2,respectively.