The invention relates to a board inserting rack synchronous drive mechanism of an ultra-soft layer board inserting machine, which is provided with a vertical tubular board inserting frame, wherein a vertical board-shaped rack inserting board is inserted into the middle position in the board inserting frame, and both sides of the inserting board are provided with teeth from top to bottom; the upper end and the lower end in the board inserting frame are fixedly connected with guide wheels respectively, and the guide wheels are meshed and connected with the board inserting teeth to ensure the traveling direction of the rack inserting board; and the lower part of the rack inserting board is meshed and connected with a transmission gear for realizing the up-and-down movement of the rack inserting board, thereby achieving the aim of inserting a drainage board underground. The synchronous drive mechanism has stable performance, large driving force and even stress and improves the convenience and the reliability in construction.