The invention relates to a method for calibrating the offset of a signal representative of a pressure (P_brut) in the combustion chamber (2) of a thermal engine, a cylinder pressure sensor (4) being provided in the combustion chamber (2) and connected to a calibration unit (7) including a means for acquiring and a means for processing the pressure signal (P_brut) and memory. The method comprises: the step of acquiring (40) and storing (400) the pressure signal (P_brut) from the cylinder pressure sensor (4); a first processing step (41) for processing the pressure signal (P_brut) into a filtered signal (P_filt) that is stored; a second processing step for processing the pressure signal (P_brut) for obtaining a filtered signal of the absolute value of the derivative of the pressure signal (I P' brutl filt) that is stored; and a third processing step (45) for obtaining a pressure signal with an offset correction (P_corr).