Aiming at the lack of universal software for spacecraft RPO (rendezvous and proximity operations) mission planning, the RPO planning model and software were studied. The concept of RPO element was proposed, and an element system, which consists of four categories (rendezvous, proximity, companion flight, and departure) was constructed. RPO missions can be formed by combining multiple elements. A mission planning model for RPO elements was established. Calculation formulas for the mission control segments, stop conditions, control parameters, and constraints were provided. Based on the ATK (aerospace tool kit), a RPO mission planning tool was designed and implemented. Simulations were conducted using examples of GEO rendezvous and sun synchronous fly around, and the results show that the established RPO elements and software can effectively design RPO missions.