Multiple scattering effect in water clouds influences the shape and intensity of the return signals of spaceborne oceanic lidar. The contaminated signals will introduce errors into the retrieval of effective attenuation coefficient k_lidar of seawater and eventually affect the detection accuracy of seawater's inherent optical properties (IOPs). The multiple scattering effect of water clouds on spaceborne oceanic lidar signals is quantified in this paper. Two main parameters of the lidar signals from the seawater are analyzed, including the effective attenuation coefficient k_lidar and signal intensity ratio R with or without water clouds using a spaceborne oceanic lidar emulator. The results show that the lidar signals from the seawater below water clouds are both related to the cloud base height (CBH) and the cloud optical depth (COD). When the COD is less than 5, and CBH is relatively low (<2 km on average), the relative difference of the effective attenuation coefficient δ is within 30%. The δ is within 20% under the condition that the COD is less than 3 and the CBH is higher than 1.8 km. Moreover, this paper gives the relationship among R, COD and CBH. This work provides significant information for the development of a spaceborne oceanic profiling lidar.