Abstract: Carbon fiber/ bismaleimide composites have received increasing interest, owing to their excellent properties, especially their toughness under extreme working conditions. We established a micromechanical model for a finite element simulation of the micro-droplet test, which involves pulling a carbon fiber out of a bead of matrix using two moving knives acting on the bead as scrapers to quantify the interfacial properties of carbon fiber reinforced bismaleimide composites. The interfacial shear strength of carbon fiber/ bismaleimide composites subjected to different hydrothermal environments was tested by micro-droplet method to illustrate the impact of moisture absorption on their interfacial properties. Hydrothermal aging caused a reduction of interfacial shear strength, which leveled off when the immersion time in water exceeded 7 days at 71°C . A numerical simulation of the debonding process was performed based on the interface cohesive element damage model to simulate the interfacial properties of the composite and to determine the correlation between experimental parameters and interfacial properties. The simulation successfully provided essential parameters for numerical analysis of the macroscopic mechanical properties of the composite. Finite element analysis of the micro-droplet test revealed that the factors that influence the interfacial shear stress distribution are the position of the knives on the bead, thermal residual stress and hydrothermal treatment conditions