Coastal engineering faces challenges from wave impacts, making the optimization of breakwater design crucial for enhancing coastal protection. This study investigates the effects of flume width, wave height, and submergence depth under a bottom-sealed condition on the transmission coefficient ( \({K}_{t}\) ) of C-pile breakwaters, using computational fluid dynamics (CFD). Results indicate that \({K}_{t}\) increases with flume width ( \({W}_{r}\) ), and when \({W}_{r}\)  < 0.3, most cases still exhibit effective wave attenuation ( \({K}_{t}\)  < 0.5), suggesting that the effective protection range of the C-pile array can be set as three times the maximum diameter of the array. The C-pile chamber adapts effectively to varying wave heights, ensuring stable wave attenuation performance. Additionally, within the resonance period range, \({K}_{t}\) increases as the relative submergence depth ( \({d}^{*}\) ) increases, aligning with the variation trend of the chamber water level coefficient ( \({K}_{c}\) ). These findings offer valuable insights for optimizing C-pile breakwater designs in coastal and marine engineering applications.