The utility model discloses a M -bus communication overload detection circuitry, including comparator, controller, reference voltage regulator circuit and current sampling circuit, the current signal of current sampling circuit sampling M -bus bus converts the syntropy input that voltage signal inputed the comparator into, standard voltage passes through in the source reverse input end of reference voltage regulator circuit output reference voltage to the comparator, output M -bus overload detection signal to the controller of comparator. The utility model discloses an unsteady too big erroneous judgement problem that leads to the fact of the total line voltage of M -bus has effectively been avoided to the overload circumstances that adopts the mode that detects M -bus bus current signal to determine the M -bus bus, adopting reference voltage adjustment circuit regulation reference voltage, can carrying out the reference voltage adjustment according to the particular case and the circuit characteristic demand of M -bus bus, the commonality is good, adopt special comparator to carry out the comparison of circuit voltage, the consumption is little, effectively prevents the damage of device.