In gas-liquid mass transfer processes，Marangoni convection may occur due to the surface tension gradient produced by mass transfer near the interface.With a falling soap film tunnel and the Schlieren optical method，the Marangoni convection patterns along the film surface were observed directly in the desorption process of acetone from the falling soap film.The Schlieren images showed the regular roll convection in the thin falling soap film during the acetone desorption.The hydraulic characteristics were determined experimentally by measuring the variation of acetone concentration in the film and the surface tension of the soap liquid.The results show that the acetone concentration gradient vertical to the falling direction is very small because the thickness of the soap film is in the order of 10-6 m.The variation of acetone concentration along the falling film is large，so there is a significant surface tension gradient，resulting in the Marangoni roll convection.The experimental results and a qualitative analysis may be helpful to understand the mechanism of Marangoni convection near the interface in the mass transfer.