Ari-launch can significantly improve rocket payloads, reduce the number of rocket launch sites and the high maintenance funds, and shorten the launch cycle. In this paper, the influence of the initial state of air-launch on the payload of the launch vehicle is studied, and the mathematical model of the rocket flight is first established by the model of the flight orbit, and then the influence of the launch height and the firing velocity on the payload of the rocket after entering the orbit is analyzed quantitatively. The results show that if the emission height and emission velocity are increased, the payload will increase obviously, and the basic emission height and emission velocity are linearly related to the payload respectively. Relative to ground launches, if the initial height reaches 30-kilometer, the payload is increased to 1.63 times, and if the initial height reaches 30-kilometer and the initial speed reaches 1000 meters per second (about Mach 3), the payload will be 5.43 times the traditional ground launch. From the point of view of initial height and speed, the effect of initial emission velocity on the increase of payload is more significant, so we should pay more attention to the increase of launch speed when designing the launch platform under the consideration of economy.