The invention discloses a method and system for synchronously treating oil shale dry distillation wastewater and garbage leachate, and belongs to the field of water treatment. The method comprises the following steps that suspended solids and oily substances, subjected to adjustment through an adjusting tank, in oil shale dry distillation wastewater are removed by means of oil separation sediment precipitation, cavitation air floatation and dissolved air flotation treatment; the treated oil shale dry distillation wastewater is mixed with the garbage leachate to be uniform according to the predetermined proportion; the mixed wastewater is added to an activated sludge system for aeration biochemical treatment, and contaminants such as ammonia nitrogen and organic matter in the wastewater are removed. According to the method and system for synchronously treating the oil shale dry distillation wastewater and the garbage leachate, the oil shale dry distillation wastewater and the garbage leachate which are similar in water quality and complementary are synchronously and efficiently treated by means of the activated sludge system, the problem that the dry distillation wastewater lacks trace elements is solved, poisonous and harmful substances in the garbage leachate can be effectively diluted, and the stability of a biochemical system is enhanced; meanwhile, the technological process is simplified, the occupied area is saved, and the construction cost and the operating cost are reduced.