The invention belongs to the field of a lithium ion battery material, and discloses an electrolyte additive and an electrolyte comprising the additive, and a lithium secondary battery. The electrolyteadditive is 4-methyl-N-tosyl benzene sulfonamide. A cyclic carbonate solvent and a linear carbonate solvent are mixed, and then are subjected to purification, impurity removal and dewatering, and a conductive lithium salt is added in the room temperature condition to obtain a common electrolyte; and next, an additive which accounts for 0.5-3.0% of the mass of the common electrolyte is added to the common electrolyte to obtain the final electrolyte. By taking 4-methyl-N-tosyl benzene sulfonamide as the additive of the lithium ion electrolyte, the cycle performance of the lithium secondary battery at a high pressure is improved.