A longitudinal stage separation (LSS) scheme for a parallel-arrangement two-stage-to-orbit (TSTO) vehicle is proposed and analyzed in detail, in which the orbiter moves along the upper surface of the booster. A TSTO concept comprising a waverider and a spaceplane was designed to numerically investigate the dynamic characteristics of the LSS at Mach 7. The influence of spike models assembled at the nose of the orbiter on the LSS at different angles of attack (AoA) (i.e., spike with half cone, spike with half cone-disk, and hemispheric spike) was explored. Moreover, the aerodynamic interference and characteristics were analyzed and compared for different spiked configurations. The aerodynamic interference during LSS is simple and weak, which is only associated with type VI shock/shock interaction, with rapid increases in the axial force when the shock waves of both stages converge. Furthermore, the model with a half cone spike has the best performance in drag reduction by 7%, whereas the model with a half cone-disk spike has the worst performance that increases axial force. The TSTO model with a half cone spike at AoA=0 and 5 deg is advantageous in LSS because of the high drag reduction and weak aerodynamic interference.