An improved Barrar-type intermediate orbit is proposed in this paper and an analytic solution is reached. When the special C values are applied by means of different combinations，we can obtain the analytic solution due to the J₂ or J₃ oblateness perturbation for the long-range ballistic vehicle，as well as the solution of Kepler's ellipse. This method is worth to popularize，it's application to dozens of simulative trajectories have shown that this method not only helps to simplify the whole process of calculations but also results in smaller truncation error. the range error and lateral error for the J₂ perturbation are approximately 10m while those for the J₃ are about 10mm.