The invention relates to konjac glucomannan tomato sauce and a preparation method thereof. The preparation method of the konjac glucomannan tomato sauce includes the steps: preparation of tomato pulp,preparation of ingredients and filling. Tomatoes are adopted as a main carrier, large viscosity of konjac glucomannan is utilized, saving of the use quantities of tomatoes is adopted as a starting point, and the konjac glucomannan tomato sauce is specially prepared through functions of low sugar, low calorie, blood fat reduction, cholesterol reduction and nutrition of konjac glucomannan, so thatnot only can the cost be saved, but also the product can have a unique health care function. Stevioside is utilized to replace traditional sucrose during production of the tomato sauce, and the sweetness of stevioside is 200-300 times that of ordinary sucrose, so that related health problems caused by excessive intake of sugar and calorie are overcome effectively; and in addition, inherent fishy smell of tomatoes can be removed effectively through addition of citric acid, so that the product exhibits the original taste of tomatoes, and the product quality is improved greatly. The konjac glucomannan tomato sauce belongs to healthy food without addition of food additives and preservatives.