High purity tungsten target was prepared by hot isostatic pressing technique and annealed at different temperatures. The microstructure and internal stress of high purity tungsten target were characterized by metallographic microscope, TEM, XRD and hardness tester. The results show that high purity tungsten target after vacuum annealing at 1 200℃ retains the fine grain structure obtained by hot isostatic pressing treatment, grain size does not grow but the dislocation density, lattice distortion and hardness are reduced greatly. This is due to the high purity tungsten target by hot isostatic pressing generates recovery after annealing treatment and the internal stress is released. When the annealing temperature is below 1 200℃, the internal stress of tungsten target cannot be removed completely. When annealing temperature is above 1 200℃, the grain size of the tungsten target begins to grow. So the optimum annealing temperature of high purity tungsten target prepared by hot isostatic pressing is 1 200℃.