The present invention relates to a bar stay locking mechanism of supine set side hurdle such as bed, the side hurdle makes the side hurdle body (8) move up and down using a first bar stay (13) and a second bar stay (14) which rotate around an axes corresponding to the length direction of the bed and configured with certain distance in upper and down direction, also the side hurdle is fixed at thelifting position, so as to form a locking piece (29) with hook type part (30), and an operating rod (23) which is supported on the supporting component of the first bar stay rotatably, a locking pin (21) which fastens with the hook type part is supported on the supporting component of the second bar stay, an applying force equipment (32) and a fork-shaped part (31) is installed on the locking piece towards the locking pin, a fastening part (26) which can fastens with the fork-shaped part moving relatively is installed on the operating rod. By means of the present invention, a middle connecting rod between the locking piece and the operating rod is not need, which reduces component number and assembly time, so as to reduce cost.