In order to study the wetting behavior of a liquid film on a surface with ultralow contact angle, the interference fringe method with oblique upward laser is developed. This method allows us to detect the position of contact line precisely and observe the surface profile of very thin film. The contact angle measurement is verified within from 0.007 degrees to 3 degrees. The wetting behavior of silicone oil droplet on a glass substrate is observed. The wetting process can be distinguished with three stages, such as advancing, stable ,and receding stage. In the stable stage, there are two angles near the contact line. And the two angles have opposite variations in trend. It can be seen that there are some reciprocating changes in the two angles and the thickness of the liquid film near the contact line during the stable stage, like the edge of the surf.