The embodiment of the invention provides a coexistence processing method and a device for a kernel mode protocol stack and a user mode protocol stack, and belongs to the technical field of networks. The method comprises the following steps: taking over a socket related function of a system, and using an interface specification consistent with a POSIX standard; modifying the taken-over system socket related function, and modifying a socket function corresponding to the application program, so that a kernel mode protocol stack interface and a user mode protocol stack interface are unified; and according to a preset message transmission rule, selecting to use the kernel mode protocol stack or the user mode protocol stack to process a receiving and sending message of the application program. According to the coexistence processing method and the device for the kernel mode protocol stack and the user mode protocol stack, a kernel mode protocol stack interface and a user mode protocol stackinterface are unified, coexistence of a single application and multiple protocol stacks is achieved, for application programs needing to use the user mode protocol stacks, only simple interface replacement needs to be conducted according to the user mode protocol stacks, the application program source program transplantation workload is small, and the system performance is high.