Signals sometimes increase and sometimes decrease on the experiment of laser backward detection of bubble films.To analyze this question,the detection section is divided into three parts,and three portions of signals are analyzed comparatively.So the factors which influence the signal intensity are ascertained,and the validating experiment is carried out.The results shows that the intensity of signals lie on the intensity of light backward scattering from bubble film which is related to distance and density,etc.To detect bubble film in the same distance and the same density,augmenting the distance between the laser and detector properly will favor the difference between signals having and having no bubbles,so it will favor laser backward detection of bubble films in water.