Abstract: The mechanism and effect of sodium phosphate in scheelite flotation was investigated through flotation tests and flotation solution calculation. The results indicate that sodium phosphate cannot depress scheelite flotation, and the addition of sodium carboante cannot effect the performance of sodium phosphate. However, the addition of calcite and calcium ions can strengthen the depressing effect of sodium phosphate on scheelite flotation. The solubility of calcite was higher than that of scheelite, and the addition of calcite increased the calcium ions concentration of scheelite solution, hence the depressing effect of sodium phosphate on scheelite flotation can be strengthened.