In this paper, a comparative study on fuel economy and component efficiency for a continuously variable transmission (CVT) and a 9-speed automatic transmission (AT) based parallel hybrid electric vehicles (HEV) is proposed. The features of CVT and AT are analyzed and optimal ratio control strategies for both the CVT and 9-speed AT are designed from the view point of vehicle fuel economy. Simulators are developed using the co-simulation of AVL Cruise and MATLAB/Simulink. The influences of difference shifting manners on the operation efficiencies of engine and motor in various driving modes are evaluated for the same energy management control strategy. Besides, the vehicle fuel economy is calculated and studied. It is found from the simulation results that, in EV mode, the motor efficiency of the CVT based vehicle is a% higher than that of the 9-speed AT based vehicle due to its continuous ratio change, while the vehicle fuel economy is b% lower than that of the 9-speed AT based vehicle since the CVT efficiency is relatively lower; in HEV mode, although CVT shows an advantage in improving the engine efficiency by 4.1%, 3.8% improvement of fuel economy is achieved by the 9-speed AT based vehicle for the whole driving cycle; in regenerative braking mode, the efficiency of the generator with CVT is c% higher than that with the 9-speed AT, while the recuperated braking energy by the CVT based HEV is d% higher.