The invention relates to a method for error suppression of inertial concretionary coarse alignment of a strapdown inertial navigation system and belongs to the technical field of inertial navigation. The method comprises the following steps of 1, according to current longitude and latitude of a carrier, carrying out transformation of an earth coordinate system into a navigation coordinate system, 2, driving two shafts of a rotation-type inertial navigation system to periodically rotate according to a certain rotating scheme, 3, according to angular velocity information output by a gyroscope in coarse alignment, updating a direction cosine matrix of a posture change of an inertial measurement unit (IMU) coordinate system relative to a p0 coordinate system through calculating a numerical solution of a matrix differential equation, and 4, orderly calculating solutions of matrixes to obtain a posture matrix of the carrier so that coarse alignment is finished. The method has the advantages that through an integral operation in coarse alignment, swinging and shaking-caused error components of outputs of an accelerometer of a ship in alignment of storm-caused swinging and shaking can be compensated; and through IMU double-shaft rotation modulation, an accelerometer zero-bias error accumulated over time is suppressed so that the precision of inertial concretionary coarse alignment is improved.