We reported on the effect of the phase relationship between forewings and hindwings in the dragonfly flight. The dragonfly-type ornithopters (DTOs) were developed to investigate the flapping flight. The wing span of DTO is 100 mm long. Reynolds number is the same order as Dragonfly's Reynolds number (103). Flights of DTOs with various phase relationships were recorded with a high speed video camera, and their motions were analyzed. We also visualized air flow around the wings in a wind tunnel. We demonstrated that there are phase relationships for accelerating flight(45°), low speed flight(180°), high speed flight(270°,315°).This relationship between flight and phase almost matched that of dragonflies.