The invention provides an optimization design method of a low-orbit communication and navigation enhancement mixed constellation. The method comprises the following steps: determining a satellite orbit type; determining a satellite orbit height; determining a minimum observation elevation angle; selecting constellation configuration; determining an orbit inclination angle; determining a satellite quantity; determining an orbit surface quantity and a phase factor; selecting initial ascending node right ascension in an optimized mode; analyzing coverage performance of the low-orbit communication and navigation enhancement mixed constellation; and after traversing ends, comparing all mixed constellation parameters satisfying design requirements, and selecting an optimal solution. The method has the following advantages: through combination of factors needing to be considered for design of a communication and navigation enhancement constellation at each phase, the designed low-orbit communication and navigation enhancement mixed constellation can satisfy user demands, is excellent in constellation performance, is small in satellite quantity and quite good in compatible mutual operation capability between constellations.