The distensible effect of a strip-shape bright region light reflection from curved liquid surface was discovered. When a collimated laser beam illumines the sunk curved liquid surface by two parallel wetting plate,the special reflective patterns,which correspond to the boundary light reflection,can be produced. In fact,there is the pattern with a strip-shape bright region in the center,the high visibility diffraction fringes,dark region both sides and the width of bright region become big with the increased width of the incident beam. The relation of the width of the bright region and the width of the incident beam was derived theoretically. Subsequently,the slope,the contact angle and the surface height of liquid surface were calculated. It is believed that the distensible effect of a strip-shape bright region is capable of real time characterization of curved liquid surface.