Multi-rotor systems have been developed into better performance for mature applications. Due to lift to weight balance on motor power and battery energy, they are limited in payload and flight endurance. Since gasoline power has 44 times better energy density than battery, integration of gas engine and DC brushless motor into a vertical take-off and landing (VTOL) system will gain much higher lift and longer flight duration in performance. A hybrid power multi-rotor system is designed by dual system of engine-driven quad-rotor and motor-driven quad-rotor, with contributions on lift power by gas engine and flight control, respectively. The proposed multi-rotor system is termed as Quad-in-Quad (QiQ) system. System design considerations on high thrust, reverse torque, vibration, heat dissipation, structure and weight balance are included by carefully weight reduction into fabrication. Microprocessor control system is designed and implemented to make gas engine in both directions in steady balanced operation. A preliminary flight test has completed on this dual quad-rotor VTOL.