An automatically identifying control method for main transformer overload joining-cutting load based on a running mode comprises the following steps of: automatically identifying the running mode of a bus according to bus connecting switch state information and separated running pressing plate information; identifying the running mode of a main transformer according to main transformer knife brake position information by combining the running mode of the bus; automatically identifying a running mode of a load circuit according to the knife brake position information of the load circuit; calculating power algebras of a main transformer medium voltage side and the load circuit running in the same bus and the corresponding node power unbalance, and checking the identification result of the running mode; detecting the main transformer overload and determining the load to be cut according to the overload degree; and cutting the load circuits from the load circuits meeting the cutting conditions according to a cutting priority. By the method, the running mode of a transformer substation is automatically identified, so that the load cutting accuracy and effectiveness of a main transformer overload joining-cutting device are ensured.