Combining the GRO (Global Navigation Satellite System Radio Occultation) and LRO (Low Earth Orbit Radio Occultation) techniques to probe the Earth's atmosphere is a main development direction of RO (Radio Occultation). In this study, the mathematical criteria of a RO event have been described. Then the effects of the main orbit parameters of LEO satellite on the RO events amount and their global distribution have been discussed by a simulation study. The results showed that:the lower the LEO satellite orbit is, the more GRO events are; when the inclination is between 30° and 75°, there are more GRO events and their Earth coverage is higher. The LRO events distribute on the Earth evenly when the LEO-LEO RO satellite set in the polar orbits. This study can provide a scientific reference for GRO and LRO satellite constellation design.