The present invention belongs to the technical field of sports equipment, and especially relates to a sit-up auxiliary device. The sit-up auxiliary device comprises a bottom plate internally providedwith a cavity and an elastic pad and a leg pressing mechanism which are arranged on the bottom plate; the cavity in the bottom plate is internally provided with a wind-up roll, one side, close to theleg pressing mechanism, of the elastic pad passes through a strip-shaped hole arranged on the bottom plate and is rolled on the wind-up roll, and a drive unit drives the wind-up roll and winds the elastic pad to regulate the distance between a user and the leg pressing mechanism; the leg pressing mechanism comprises a baffle arranged on the bottom plate, the baffle is provided with an upper platesurface being parallel to the bottom plate and is provided with a support roll and an upper pressing roll arranged in order in the direction being far away from the bottom plate, and the baffle is provided with a flexible fixing unit configured to regulate the distance between the upper pressing roll and the support roll. The sit-up auxiliary device employs the elastic pad and the wind-up roll arranged at the inner cavity of the bottom plate to cooperatively regulate the distance between the user and the leg pressing mechanism to conveniently and rapidly regulate comfortable exercise positionsaccording to users with different body shapes.