A method for determining an equivalent velocity of a satellite for SAR imaging, characterized in that the method comprising: establishing a geocentric rotation coordinate system, and acquiring, according to a running track of a satellite, a plane closest to the running track of the satellite under the geocentric rotation coordinate system so that a quadratic sum of distances from respective points on the running track of the satellite to the plane is minimum; establishing a circular arc track model in the plane and acquiring a circular arc track closest to the running track of the satellite in the circular arc track model; determining, according to the information of the circular arc track, an equivalent velocity of SAR imaging of the satellite, wherein the step of determining, according to information of the circular arc track, an equivalent velocity of SAR imaging of the satellite comprises: setting related parameters, the related parameters include: a point target on an earth surface track, set as T; a point S, set as the middle point of the circular arc track; the circle center C of the circular arc track, set as the origin of a coordinate system; then the coordinates of the point target T satisfy the following expression: T → = 0, R c cos β e, R c sin β e T; where R c is the distance from the origin of the coordinate system to the point target T; β e is ∠SCT; During the data acquisition time, the coordinates of the position S' of the satellite satisfy the following expression: S → ⁢ ʹ = r sin ω s ⁢ τ, r cos ω s ⁢ τ, 0 T; where ω s is the angular velocity of the satellite on the circular arc track; τ is the azimuth time; r is the radius of the circular arc track; then an instantaneous slant range ( R (τ)) satisfies the following expression: R τ = S ⁢ ʹ ⁢ T → = r sin ω s ⁢ τ 2 ⁢ r cos ω s ⁢ τ - r cos β e 2 + R c sin β e 2 = r 2 - 2 ⁢ r ⁢ R c cos ω s ⁢ τ cos β e + R c 2; according to a method of small angle approximation, the expression for the instantaneous slant range ( R (τ)) is simplified into the following expression: R τ = r 2 + R c 2 - 2 ⁢ r R c cos β e + r R c ω s ⁢ τ 2 cos β e = r 0 2 + v r 2 ⁢ τ 2; where r 0 is the shortest slant range, v r is the equivalent velocity and v r satisfies the following expression: v r = r R c ω s 2 cos β e. establishing a geocentric rotation coordinate system, and acquiring, according to a running track of a satellite, a plane closest to the running track of the satellite under the geocentric rotation coordinate system so that a quadratic sum of distances from respective points on the running track of the satellite to the plane is minimum; establishing a circular arc track model in the plane and acquiring a circular arc track closest to the running track of the satellite in the circular arc track model; determining, according to the information of the circular arc track, an equivalent velocity of SAR imaging of the satellite, wherein the step of determining, according to information of the circular arc track, an equivalent velocity of SAR imaging of the satellite comprises: setting related parameters, the related parameters include: a point target on an earth surface track, set as T; a point S, set as the middle point of the circular arc track; the circle center C of the circular arc track, set as the origin of a coordinate system; then the coordinates of the point target T satisfy the following expression: T → = 0, R c cos β e, R c sin β e T; where R c is the distance from the origin of the coordinate system to the point target T; β e is ∠SCT; During the data acquisition time, the coordinates of the position S' of the satellite satisfy the following expression: S → ⁢ ʹ = r sin ω s ⁢ τ, r cos ω s ⁢ τ, 0 T; setting related parameters, the related parameters include: a point target on an earth surface track, set as T; a point S, set as the middle point of the circular arc track; the circle center C of the circular arc track, set as the origin of a coordinate system; then the coordinates of the point target T satisfy the following expression: T → = 0, R c cos β e, R c sin β e T; where R c is the distance from the origin of the coordinate system to the point target T; β e is ∠SCT; During the data acquisition time, the coordinates of the position S' of the satellite satisfy the following expression: S → ⁢ ʹ = r sin ω s ⁢ τ, r cos ω s ⁢ τ, 0 T; where ω s is the angular velocity of the satellite on the circular arc track; τ is the azimuth time; r is the radius of the circular arc track; then an instantaneous slant range ( R (τ)) satisfies the following expression: R τ = S ⁢ ʹ ⁢ T → = r sin ω s ⁢ τ 2 ⁢ r cos ω s ⁢ τ - r cos β e 2 + R c sin β e 2 = r 2 - 2 ⁢ r ⁢ R c cos ω s ⁢ τ cos β e + R c 2; according to a method of small angle approximation, the expression for the instantaneous slant range ( R (τ)) is simplified into the following expression: R τ = r 2 + R c 2 - 2 ⁢ r R c cos β e + r R c ω s ⁢ τ 2 cos β e = r 0 2 + v r 2 ⁢ τ 2; where r 0 is the shortest slant range, v r is the equivalent velocity and v r satisfies the following expression: v r = r R c ω s 2 cos β e.