Abstract: To alleviate pressure fluctuation inside a Francis turbine draft tube working under part-load operation, a fin installed on the wall of the conical part is one effective method in engineering application. This paper investigates the effects of fin installation on the internal flow and pressure fluctuation inside the draft tube based on numerical calculation. Results show that a fin can change the velocity and pressure distribution around the fin. Further, the fin affects the vortex evolution in draft tube and consequently changes vortex rope and pressure fluctuation. Under non-cavitation condition, an extra small vortex rope occurs near the fin, which plays the role of pressure stabilizer and decreases the pressure fluctuation amplitude in the conical part. It is the interaction of the extra small vortex rope with the vortex rope in mainstream results in the complicated flow in the elbow part of the draft tube. As a result, in the elbow, there is a slight increase of pressure fluctuation amplitude. Under cavitation condition, the fin reduces the size of both vortex rope and cavity, and suppresses the pressure fluctuation in the whole draft tube.