Abstract: Based on comet observations from JPL (Jet Propulsion Laboratory) and MPC (Minor Planet Center), the orbits of long period comets (LPC) were reverse-evolved to obtain their original orbits. The dynamic characteristics of LPC observation orbit and original orbit are analyzed. The results show that the distribution of reciprocal of the semi-major axis of LPC observation orbit ((1/a)obs) is significantly different from that of the original orbit ((1/a)_ori), and the peak values are at (1/a)_obs ~2 × 10^-5 au^-1and(1/a)ori ~6 × 10^-5 au^-1, respectively; large perihelion LPC (perihelion distance q > 3.1 au) and small perihelion LPC (perihelion distance q ≥ 3.1 au) have the same peak position of original orbit ((1/a)_ori),both located at1 × 10^-4 au^-1; the peak positions of original reciprocal semi-major axis of LPC between JPL and MPC are the same, both at 1 × 10^-4 au^-1. Many Oort cloud comets have large perihelion distances (more than 50% of comets with q > 3.1 au). It will provide information to understand the dynamical characteristics of long period comets and Oort cloud comet, and will also provide a research basis for future space missions targeting long period comets.