【Aim】 To investigate the nectarrobbing behavior of Megachile (Xanthosaurus) japonica Alfken on its nectar plant Thermopsis lupinoides (L.)in Mu Us sandland, Inner Mongolia.【Methods】 During the flowering season of T. lupinoides, we investigated the main pollinators and observed the robbing behavior of M. japonica on T. lupinoides, and recorded the position of holes in the corolla tube chewed by robbers at the base of flowers near the nectar spur. 【Results】 M. japonica is the dominant pollinator of T. lupinoides. As primary robbers, M. japonica bees cut a longitudinal split at the base of flowers by mandibles and obtain nectar through it, while directly obtain nectar without making holes when they act as secondary robbers. They did not show an tendency to seek pre-cut robbing holes, but individuals displayed a preference for one side of the flowers. In 13 plots, the percentage of nectar robbing from blooming flowers was from 95.4% to 100%, and only reached 64.7% in buds. 【Conclusions】 M. japonica is not only the main pollinator but also the primary robber and secondary robber of T. lupinoides in Mu Us sandland.