The invention discloses an integrated optimization method for the interstage ratio thrust trajectory of a sub-orbital carrier rocket. The method comprises the following steps that: through a genetic algorithm, multiple groups of parameter combinations of interstage ratios, thrusts and sliding time are given to serve as the individual of an initial population; each group of parameter combination is independently taken as an input condition, a shift exchange speed is taken as a target function, and solving is carried out through an internal layer optimization algorithm to obtain an optimal flight trajectory and the corresponding shift exchange speed under each group of interstage ratios and thrust; and the shift exchange speed serves as the fitness of each group of parameters, and the genetic algorithm is used for obtaining an optimal vehicle interstage ratio and thrust combination and the corresponding flight trajectory. By use of the method, under a situation that dynamic pressure, overload and heat flow constraints in a flight process of the sub-orbital carrier rocket are met, when the total explosive payload of the vehicle is constant, the shift exchange speed of the sub-orbital carrier rocket can be improved as much as possible to enable an effective load to own higher shift exchange speed.