The present invention discloses a protection circuit and method for thermal printing of an electrocardiograph. The protection circuit comprises a thermal printing heating plate and a microprocessor control unit; an analog signal output terminal of the microprocessor control unit is connected with a driving amplification circuit and controls the driving amplification circuit; the driving amplification circuit drives conduction degree of a MOS power tube and provides the heating plate with DC power; a current sampling resistor is disposed at a power grounding side of the thermal printing heating plate; and sampled current signals are connected to a second analog-to-digital conversion input terminal of the microprocessor control unit. Various methods and circuits are used to prevent abnormal system power supply of the whole machine due to overhigh printing current and to prevent the heating plate from being burnt due to the fact that current through the heating plate is overhigh and temperature of the heating plate is overhigh. Overheating protection of a thermal printer can be more reliable due to arrangement of hardware circuits and software regulation and management.