The invention discloses an ultra-thin unit cell for a thermal battery and a preparation method thereof. The ultra-thin unit cell for the thermal battery comprises a heating sheet, an anode sheet, an isolating sheet and a cathode sheet, which are overlapping in sequence, wherein thickness of the unit cell is 0.6-1mm. The scheme of the invention is favorable for improving high power discharges of the thermal battery and increasing activation speed of the thermal battery.