The utility model discloses a high -efficient burning boiler of low -BTU gas, include boiler body, be located the left combustor of boiler body with be located the air heater on boiler body right side, boiler body includes the barrel, is located the inboard stove courage of barrel, be located left side below the combustion gas interface, be located right side below the room of strile -bacing, be located the top the two -return tobacco pipe, be located the third return stroke tobacco pipe of two -return tobacco pipe top, be located before left the smoke box and be located the back smoke box on right side, air heater through a flue with boiler body connects. Beneficial effect: the low -BTU gas causes the huge energy extravagant because surely the flame is difficult, and for a long time directly discharges, and through these project research and development, the accessible boiler directly burns, for enterprise's saving running cost.