Lidar has been used for ocean remote sensing widely. The upward laser beam is distorted due to the rough sea surface. It limits dramatically laser transmission through sea surface and the application of Lidar under water. The beam distribution of upward laser beam through sea surface is studied based on the geometric optical theory,three dimension wave simulation and Monte Carlo simulation respectively. Results show similar beam distribution by the three methods. The beam profile is limited in ±10° for collimated vertical upward beam. Demonstration of beam distribution through man-made rough water surface is conducted in a water tank. Results show that the exit angle is actually limited within ±10°. The study will be useful to the design of Lidar application under sea water.