The invention discloses a thick film heating device for an automobile water tank. The thick film heating device comprises a plastic substrate; the interior of the plastic substrate is of a cavity structure; a water groove is arranged at the inner bottom of the plastic substrate and is composed of a plurality of S-shaped groove bodies which are sequentially connected end to end; a water inlet is formed in one side of the plastic substrate; a water outlet is formed in the other side of the plastic substrate; the water inlet communicates with one end of the water groove; the water outlet communicates with the other end of the water groove; a plastic base plate covers the plastic substrate; a second sealing rubber ring is arranged on the inner peripheral surface of the plastic substrate; a first sealing rubber ring is arranged on the inner peripheral surface of the plastic substrate; a stainless steel thick film heating body is arranged in the plastic substrate and is arranged on the water groove; and the plastic base plate covers the stainless steel thick film heating body. The thick film heating device has the advantages that the structure is compact, the working stability is good, the operation is convenient, the production efficiency is high, the safety performance is reliable, the heating efficiency is high, and the heating time can be greatly saved.