In order to predict the unsteady thrust of the interaction line spectrum of the pump jet propeller rotor and the periodic leading vane wake, ignored the thickness of the pump jet propeller rotor blades, and simplified the pump jet rotor into an annular cascade. According to the sheet theory, the radius that is the segment of the pump jet rotor was intercepted at r, and the change of the flow field parameters along the segment radial was ignored. Therefore, the annular cascade segment can be considered as a planar cascade, and the periodic inflow is considered based on the interaction between the planar cascade and the harmonic wave. The unsteady excitation force of the interaction line spectrum between the front guide vane segment and the rotor segment is derived. The unsteady thrust line spectrum prediction formula is obtained through the circumferential integration of the rotor segment. The validity of the formula is verified through numerical and experimental methods. A design parameter impact analysis was conducted, and it was found that when the ratio of the current guide vane rotor spacing to the chord length of the front guide vane is greater than 1, the rotor rear guide vane spacing has almost no impact on the excitation force line spectrum thrust of a single rotor blade.