The relationship between parameters of airborne laser bathymetry (ALB) and its maximum penetration depth is discussed. The minimum detectable signal-to-noise ratio is taken as the criteria of choosing parameter. The performance of ALB in daytime and nighttime is evaluated, and the relationship between maximum penetration depth and transited peak power, receiver aperture, angle of field-view, and spectral bandwidth is demonstrated. The ALB system with the chosen parameters has a penetrability of 49 m in daytime and 65 m in nighttime. It is matched the requirement of costal charting and rack detection.