The invention discloses a method for improving HTO thickness stability. In the furnace tube HTO machine table normal technological process, when the accumulated film thickness reaches a certain numerical value, a new circulation cleaning form automatically runs, a high-low temperature/pressure simultaneous switching manner is adopted in the new circulation cleaning form, under the high pressure and high temperature condition, different vapor pressures are used for converting chlorine containing by-products into gaseous state matter to be brought out, and the effective removing effect is achieved. By means of the method, the by-products at the bottom of a technological cavity can be effectively removed, and the machine table film forming technological thickness stability is guaranteed.