Phosphatidylcholine monolayer films are studied under different physics conditions by LB technique.Meanwhile,analyze the quality of deposition monolayers and molecules' orientations. Base on this,we also studied the phase separation of complex consisting of phosphatidylcholine and cholesterol.By AFM,we character the molecular structure and orientations.The results show that the formation of phosphatidylcholine monolayer film is related to the physics conditions including density,temperature,pH,phosphatidylcholine molecule can form complexes with Cholesterol.We can obtain the specific structure of LB monolayers by choosing proper conditions.