The positive characteristics observed in terms of compact structural sizes and high torque-transmitting capacities have allowed co-rotating twin-screw (CRTS) gear transmissions to be extensively applied to instances requiring small central distances and large power densities. In this study, a multi-objective optimization model for the quick determination of structural parameters of the CRTS gear transmission system is proposed based on the heuristic search and non-dominant sorting genetic algorithm. Results reveal that the optimized scheme with 17 design variables and 18 constrained parameters can be achieved with this model. The system reduces mass by 7.74 % from the original mass of 199.06 kg, while the safety factor variance of the transmission system decreases by 29.3 %. This method applies to other transmission systems with different structures and thus provides general theoretical support for modern gear transmission optimizations.