Abstract: The fluid-structure coupling model of the fluid discharge over a rectangular thin plate weir was established, and the calculation program was finished. The results, which include deformation of the weir under static pressure drop of liquid and discharge height, are coincided with those gained from the commercial software at the same calculation conditions. The program was verified. The influences of the fluid level, Young’s modulus of elasticity and input flow on the stability of the rectangular thin plate weir under the fluid discharge over condition were computed. The FSCP-FP program is simple to set up and its calculation is fast, which can be used to estimate fleetly the stability of the rectangular thin plate weir when the fluid discharge is over it.