Studies the leaching rates of NaOH for scheelite. Through high temperature and high pressure alkaline leaching tests on two types scheelite (A and B), investigates the instability cause of the leaching rate of scheelite. The analytical results from SEM, XRD and XRF show that A and B scheelite have basically the same phase structure, but different elemental composition. B ore contains pyrite ore with oily smooth surface, while A ore contains no pyrite and has loose surface. Under the same experiment, A and B scheelite have leaching rates of 98.4 % and 66.4 % respectively. The analytical results from SEM and XRD of the tungsten residue show that the scheelite of A ore decomposes completely, while B ore doesn't and the original form still exists in the slag. The research shows that the oily smooth surface of B scheelite is due to the presence of pyrite, which makes lye difficult to access scheelite interior and prevent mineral leaching.