The invention relates to an extensible modular small-sized controller device. The extensible modular small-sized controller device comprises an upper cover and a base; at the middle of the extensible modular small-sized controller device, a CPU module, a communication module, a signal conversion module, a driving module and a power source module are connected through a system bus and a user bus; and long pin type plugging pins of plugging pin structures and sockets are in plugging connection in a stack manner so as to form the system bus and the user bus. The extensible modular small-sized controller device of the invention can conveniently realize resource extension and can meet control requirements of different control objects; the stack type plugging connection structure is adopted, so that the extension operation of the device can be made to be simple and easily feasible; a modular design is adopted, so that the structure of the whole device is simple and clear, and the device is easy to use and maintain; the modules are connected through the system bus and the user bus, so that the number of user buses required by interface resources can be configured through setting the states of programmable logic switches, and the reasonable allocation and effective management of user bus resources can be realized.