In the present paper the width effect of isogyres on convergence polarization interference diagram of crystals with high refractive index and large optical angle are considered. By increasing tho deviation angle of isogyres from vision field of polarization microscope and obtaining the solution of deviation angle of isogyres hyperbola from vision field. The precision of optical orienting is increased significantly. The theory of isogyres involving tho width effect is demonstracted and the accurate isogyres hyperbola deviating from leaving or oonteoting with vision field is obtained and confirmed by experiment. It is shown that this orientation method for crystals with, large optical angle is convenient, best and valid.