Abstract: The trajectories of the Chinese Jovian mission is designed. Gravity assist is needed to achieve circumjovian missions, for current launch capability is not enough. With the launch window between 2029 and 2032 and the flight time not exceeding 7 years, the trajectory with gravity assists and impulsive maneuvers is formulated by some parameters such as the time of launch, gravity assist, maneuver and arrival, and the Particle Swam Optimization(PSO) algorithm is applied to optimize these parameters so that the total velocity increment is minimum. After entering Jovian system, the spacecraft is captured to a big circumjovian elliptical orbit by using gravity assist of the Ganymede. And then resonant gravity assist orbits are constructed to capture the spacecraft to the orbit of the Callisto. Based on the Jovian mission, an expansion mission of Uranus flyby was considered. The Uranus detector, which is released from the Jovian system detector when arriving at Jupiter, will fly to the Uranus after Jovian gravity assist with no fuel consumption and flied by Uranus before 2043,it can provide reference for the future task of deep space exploration in China.