The formation and pinch-off of leading vortex ring in the starting jets with uniform background crossflow have been investigated numerically for Rv from 3 to 12and ∞,where Rv is the ratio of the jet velocity Uj to the velocity of background crossflow Uc. Rv = ∞ represents the case without any background crossflow. The background crossflow disrupts the symmetry in the formation process of leading vortex ring, causing it to move laterally and the circulation strength on either side of it to be unequal. The difference in the circulation strength can be normalized based on slug model. The lateral movement introduced by crossflow is found to be inversely proportional to Rv,but directly proportional to Uc at aconstant Uj. A kinematic model based on the lateral movement of leading vortex ring is established to characterize the pinch-off process in the starting jet with background crossflow. The occurrence of pinch-off at Rv ≥ 12 remains consistent with that without background crossflow, i.e., the formation number F remains constant with Rv. As for smaller Rv (less than 12), F increases linearly with Rv,i.e., F ∼ C2Rv,where C2 is a constant.