This paper reports the combustion and smelt production of semichemical pulp spent liquors (solid matter content 54.9%) as using heavy oil of auxiliary fuel by spray method and the calorific value's estimation of mixture of spent liquor solids and lignin as auxiliary fuel. Semichemical pulp spent liquors were burnt well and smelts were produced and flowed out successfully. The principal components of smelts are Na2C03, Na2S and sulfidity of white liquor will become 2430%, if Na2CO3 in green liquors are caustisated. It was estimated that the calorific value of mixture is equal to, or more than kraft pulp black liquor solids.