Abstract: In order to achieve the orbit maneuver and save the fuel consumption in the space travel mission of spacecrafts, the dynamic equations and performance index functions of aero-gravity assist (AGA) maneuver were established under the terminal constraints and path constraints. The continuous two-point boundary value problem was converted to the equivalent nonlinear programming problem using the pseudospectral method, and the optimal trajectories corresponding to the maximum and minimum heliocentric velocities of the spacecraft were obtained with SNOPT software. Finally, a simulation was made for the trajectory optimization algorithm, and the variation of optimal trajectories under the peak constraint of heat flow rate was obtained. The results show that the maximum velocity deviation is 0.009 m/s when the number of nodes is 40, which satisfy the convergence precision demand. In the AGA maneuver, the maximum heliocentric velocity increases by 8.02%, the minimum heliocentric velocity reduces by 32.26%, and the corresponding deflection angles increase by 42.74° and 68.40°, respectively, when compared with those in the gravity-assist orbit maneuver. When the peak heat flow rate is 500 W/(cm2·s), the depth of spacecraft into the atmosphere, the heliocentric velocity, and the deflection angle reduce 6.35 km, 93 m/s, and 6°, respectively, compared with those without heat flow rate constraint.