Sulfonated treatments commonly used in deep-well water-based drilling fluids have significant biotoxicity without exact sources，which lead to the restriction of environmental protection regulations. To solve this problem，the relationship between the physicochemical characteristics of typical sulfonated treatments，such as functional groups，content of heavy metals and organic poisons，particle morphology，and their biotoxicity was analyzed. The results showed that the sulfonic acid groups in agents were not biotoxic，and the traces of heavy metals and organic toxicants were negligible factors. The removal of residue by dialysis through a semi-permeable membrane and the followed separation of water-soluble components using a Soxhlet extractor made the treatments biologically non-toxic，further demonstrating the predominate contribution of residual sulfonating agents （sodium bisulfite and sodium metabisulfite）and the adsorptive inactivation of solid-phase large particles dispersed in water on the Vibrio fischeri to the biotoxicity. Finally，the sulfonated agent was depolymerized using a homemade MOF. When replacing the sulfonated treatment agent in the sulfonated drilling fluid with the biologically non-toxic treated agent，the rheological properties of the drilling fluid were basically unchanged，the API and HTHP filtration loss only increased slightly. The sulfonated drilling fluid system realizes biological non-toxicity，which provide a powerful technical support for the application of sulfonated treatments.