Leucospis gigas Fabricius, one of the largest body-sized species in Chalcidoidea, does a great harm to some wild solitary bees. After first discovering its damage to Megachile (Chalicodoma) desertorum Cockerell, an important pollinator for many plants in West Erdos Region, we studied its life history, activeregulation of adults, host range and oviposition behavior. The results showed that L. gigas propagated 1 generation a year and reproduced by parthenogenesis; the female's life-span was about 35 days and mid-June was the active peak of adults; it parasitized only the matured larvae; the oviposition behavior could be divided into 3 steps: searching host nests, choosing the oviposition place, and extending the ovipositor stylets and laying eggs.