As a chemical cold production technique in heavy oil reservoirs, emulsification viscosity reduction flooding can effectively decrease the viscosity of heavy oil and improve the development efficiency of heavy oil reservoirs. Based on the self-developed anionic/nonionic emulsification viscosity reduction system for heavy oil cold production, the variation of molecular composition of heavy oil before and after viscosity reduction were analyzed by means of four-component separation experiment and microscopic characterization of heavy oil. Atomic force microscopy techniques were employed to systematically study the microscopic mechanisms of the interactions between heavy oil components in the emulsification viscosity reduction system. The research results demonstrate that the viscosity reducer molecules can form stronger hydrogen bond interactions and π-π stacking interactions with heavy oil components, weakening the hydrogen bond interactions between colloids and asphaltenes. After viscosity reduction, the colloidal structure of heavy oil transforms from a smooth surface to a block structure with numerous small pores, while the asphaltene structure becomes loose, accompanied by the shedding of irregular granular substances. The emulsification viscosity reduction system can significantly reduce the adhesion forces between colloids or asphaltenes, with the maximum adhesion force decreasing from 5.49 nN and 3.11 nN to 0.5 nN and 0.8 nN, respectively. With increasing concentration of the viscosity reduction system, electrostatic repulsion forces between heavy oil components, represented by asphaltenes, emerge, along with enhanced spatial steric repulsion forces. The dynamic equilibrium of aggregate clustering is altered, with the average distance between asphaltene linking branches increasing from 5.43 nm to 11.14 nm, and the graft chain length increasing from 1.84 nm to 6.22 nm, thereby facilitating the reduction of the strength of the three-dimensional network structure formed by heavy oil asphaltenes and lowering the viscosity of heavy oil. The research results have important guiding significance for clarifying the viscosity reduction mechanism of emulsion viscosity reduction system and the application of heavy oil cold production technology in oilfield development.