Increasing attention has been paid to near space plane in recent years. In the present study, a multi-module RDCRC (rocket dual combustion ramjet combinedcycle) engine was proposed to power the near space plane and its performance was analyzed. The plane was designed to drop at about Mach 0.8 and 10 km above sea level. Under the gravity and the combination thrust of the engine, the plane accelerates to about Mach 2 at 5~8 km above sea level. Then, it climbs up and accelerates the near space under the ejector-ramjet mode or DCR ramjet mode. The ejector-ramjet mode provides higher acceleration with less efficiency, while the DCR ramjet mode provides more efficiency and lower acceleration, thus the mode can be transformed according to the actual situation. Finally, the plane climbs up to about 26 km above sea level, accelerates to Mach 6, and starts to cruise in DCR scramjet mode. A trajectory optimization was carried out for air launch and surface launch, and the obtained results show that the air launch can save about 37% propellant with Mach 6 and 26 km above sea level, and there lies a negative optimal initial flight angle that leads to an optimum ratio between the residual mass and the initial mass.