To research the airborne liquid cooling system, this paper uses software Simulink to build the mathematical model of each component in the single-branch series connection system and multi-branch parallel connection system. The characteristics of systems are compared and analyzed. PID control is used for branch flow regulation in multi--branch system, and the dynamic simulation of multi-branch system is subsequently performed under given conditions. Moreover, the influence of avionics operating condition, flight altitude and flight Maher number on the system is analyzed. The result shows that the flow resistance of multi-branch system is lower, the flow of each branch is carried out according to the thermal load of the electronic equipment in different working conditions in multi-branch system, and a lower flight altitude or a larger flight Mach number will lead to a higher temperature of system.