The work aims to investigate the influence of grain boundary at different angles on the friction properties of monolayer polycrystalline molybdenum disulfide (MoS2) nanosheets and study the corresponding friction dissipation mechanisms. The monolayer polycrystalline MoS2 nanosheets were prepared by chemical vapor deposition and force curve test and friction testwere taken to obtain adhesion force, friction coefficient and friction dissipation by atomic force microscope, respectively. For the monolayer polycrystalline MoS2 nanosheet, the adhesion force was 7.20 nN in the non-grain boundary region, and the adhesion forces were from 11.11 to 11.40 nN in the grain boundary at different angles. The friction coefficients of the non-grain boundary region and -6°, 33° and 88° grain boundary regions (400 nm×400 nm) were 0.006 19, 0.006 45, 0.007 37 and 0.017 60, respectively. Under normal load at the range of 30 nN~150 nN, the friction dissipations of different regions were increasing from 33.93×10-16 J to 46.88×10-16 J at the non-grain boundary region, from 37.15×10-16 J to 52.09×10-16 J at the -6° grain boundary region, from 38.76×10-16 J to 55.18×10-16 J at the 33° grain boundary region and, from 46.59×10-16 J to 59.72×10-16 J at the 88° grain boundary region. The polarity particles adsorbed at grain boundary strengthen the interaction between tip and MoS2 surface, so the adhesion forces at grain boundary are larger than that at the area without grain boundary, but angles have little effect on adhesion. Within centain test range, the friction coefficients and friction dissipations in the grain boundary regionsare larger than those in the non-grain boundary regions, and friction coefficients increase with grain boundary angles. There are discrepancies in bending stiffness of grain boundaries at different angles, which leads to different pucker effect when the probe slides through grain boundaries. Higher normal load will cause more out-of-plane deformation, causing surface pucker effect. Therefore, friction dissipation increases with grain boundary angles and normal load.