The Piano Key Weir (PKW), a novel weir, improves the discharge capacity greatly compared to the linear weir with its prolonged nonlinear overflow edge. To address the problem of insufficient discharge capacity of PKW in a proposed hydropower station, the optimized schemes of increasing the length to width ratio L/W, increasing the weir height P and decreasing the number of weir units n as well as increasing the weir height P were proposed. Then, physical model tests were conducted to obtain the optimal schemes that meet the design requirements. Besides, the influence of hydraulic model types (including overall model and cross-section model) and the scale effect of different schemes on the discharge capacity of PKW was investigated. The results demonstrate that the discharge capacity of PKW was improved to some extent but yet did not meet the design requirements in scheme M1 (L/W increased from 7.75 to 8.88); the discharge capacity increased significantly in both scheme M2 (P increased from 4.50 m to 6.50 m) and M3 (P increased from 4.50 m to 6.90 m and n decreased from 17.5 to 8.5), which met the design requirements. Additionally, the discharge capacity of the cross-section model was slightly higher than that of the overall model by about 6%, and the scale effect could be ignored when the weir head exceeded 2.50 cm in the experiments.