Abstract Pattern analysis of the impact‐parameter dependent trajectory for the H + H 2 exchange reaction was performed at temperatures T  = 3 and 300 K by employing the quasi‐classical trajectory calculation on a London‐Eyring‐Polanyi‐Sato surface. We find that (a) 0.66 fraction of reactive trajectories throughout b  = 0.0 ~ 5.0 Å at T  = 3 K, while only 0.33 at T  = 300 K only for b  = 0.0 ~ 1.5 Å and decreases soon to zero for b  = 2.5 ~ 5.0 Å. (b) Ninety eight percent of the trajectories showed direct collision pattern at T  = 300 K, while at T  = 3 K, 72% for direct collision trajectories and 28% showed the intermediate H + H 2 complex formation pattern. These results suggest that nonzero impact‐parameter trajectories play a role at T  = 3 K to enhance reactivity due to long‐range attraction forces. Trajectory pattern analysis reveals a characteristic propensity rule between the amplitude of the time‐dependent interaction potential and the trajectory reactivity, thus we can judge if a trajectory is reactive or nonreactive. The analysis also proposes a roaming‐like libration motion at T  = 3 K like in the interstellar clouds.