In order to solve the problem of pulp viscosity in the modification process of sodium bentonite, the effects of sodium carbonate dosage, pulp concentration and dispersant on the effect of sodium modification and pulp viscosity were systematically studied, and the mechanism of reducing pulp concentration and adding dispersant were discussed. It is found that by reducing the pulp concentration, the “house-of-cards” structure by edge-to-edge and edge-to-face contact is obviously reduced, and the problem of pulp viscosity is improved, but the pulp quantity and the treatment difficulty increase at the same time. By adding dispersant sodium pyrophosphate, phosphate ions are adsorbed on the positive edge of montmorillonite, which increases the repulsive force between montmorillonites and reduces the viscosity of pulp, and improves the sodium effect. Through systematic experiments, high quality sodium bentonite is prepared with 0.5% （mass fraction） sodium pyrophosphate, 5% （mass fraction） pulp concentration and 5% （mass fraction） sodium carbonate. In this condition, the swelling index and colloidal value of bentonite have been greatly improved, the colloid value of sodium bentonite increases from 95 mL/15 g to 975 mL/15 g, and the swelling index increases from 8 mL/2 g to 25 mL/2 g after 1.5 h sodium modification.