The invention discloses a flight path simulation method of a variable-parameter missile-borne bunching SAR in a locking mode. The method comprises the steps of 1 determining four coordinate systems adopted in simulation, 2 obtaining a conversion matrix between the coordinate systems, 3 setting radar system basic simulation parameters, 4 obtaining a rough simulation flight path coordinate matrix of a missile body in a flight path plane-coordinate system Em through the Runge-Kutta method, 5 obtaining a rough simulation flight path coordinate matrix of the SAR in a earth rotating coordinate system Eg within synthetic aperture time, and 6 obtaining an accurate missile body simulation flight path. The invention provides the locking work mode of the variable-parameter missile-borne bunching SAR, and the special fixed squint angle of the mode brings convenience to missile guidance.