Restraint of background noise, for example water interference, is an important problem for laser backward detection of bubble films in water. The problem was analyzed and an experiment was carried out. The powers of light backward scattered from water and bubble film were measured when the distances between the laser and the detector were changed, and the data were analyzed by comparison. The results show that moderately increasing the distance between laser and detector will favor restraint of water backward scattering light interference and will enlarge the difference between signals having and having no bubble films, so it will improve the laser backward detection capability of bubble films in water.