The invention discloses a method and system for extending orders of spherical cap harmonic models of earth disturbance gravity fields. The method comprises the following steps of: in an aircraft launching process, determining a spherical cap radius by taking a launching first area as a to-be-approached spherical cap area; determining a spherical cap boundary condition according to the spherical cap radius; and according to the spherical cap boundary condition, circularly calculating a zero root value of an associated Legendre function, and when a distance between zero root values obtained viatwo adjacent calculations is smaller than a preset limiting value, ending the calculation, namely, realizing the extension of an order of a spherical cap harmonic model of an earth disturbance gravityfield. According to the method and system, orders of spherical cap harmonic models are extended to a certain extent, assignment precision of along-track disturbance gravity of spacecraft is improved,and benefit is brought to accurate navigation.