Abstract: Because of the long integration time of Medium Earth Orbit SAR (MEO SAR), the hyperbolic range equation based on linear trajectory module is not suit for MEO SAR. Considering this issue, a high-order modified hyperbolic range equation is proposed. Incorporating with an additional linear component and quartic component, quartic Taylor series expansion of it has exactly the same value as which of the actual range history of MEO SAR. Then, the two-dimensional spectrum based on high-order modified hyperbolic range is analytically derived by using an approximate azimuth stationary point, based on method of series reversion the accuracy of the two-dimensional spectrum is analyzed which is exactly equal to quartic phase term. Simulation results show that the proposed range equation and the two-dimensional spectrum are accurate which can give fine resolution imagery with the entire aperture.