The basic design method and advantage of conformal antenna are introduced in this paper. A novel design of dual-band conformal co-aperture antenna for airborne navigational application has been completed. This antenna operates at L band and C band with two RF output ports. A new realization way of antenna aperture synthesis has been found through the comparative analysis of different ways of antenna integration. The model of the antenna is simulated, and a prototype is fabricated and measured. The simulation and measured results are in good agreement. The gain of L-band beyond -1dB at the domain range pitch angle 60°~ 95° and azimuth angle -45°~45° and the gain of C-band beyond -2dB at the same time.