The alkali-surfactant-polymer (ASP) flooding as one of efficient enhanced oil recovery technology has attracted great interest in the recent years. Nevertheless, the high stability of the oily water has become a threat to the environmental security. And most of the separation methods have been gained through trial-and-error approaches at present. However, there is a lack of clear microscopic scale study with respect to the mechanisms that govern the separation efficiency. In this paper, the effects of alkali (A), surfactant (S) and polymer (P) on the coalescence behavior of oil droplets are experimentally investigated with high-speed photography. The results indicate that the composition of the ASP flooding solution substantially influences the coalescence patterns of oil droplets. The optimum solute concentration of each component in ASP for oil droplet coalescence is obtained based on the microscopic experimental results. Statistical investigation on contact angles of the coalesced oil droplets is concluded that effective contact angles are distributed asymmetrically within the ranges of conditions studied. And most of the oil droplets are found to coalesce at small contact angles (5-25) or large contact angles (50-80 degrees). The research findings are of great significance for developing high-efficient processing technology for ASP flooding produced water.