Due to the elastic optic and electro optical effect of lithium niobate and lithium tantalite, they can be applied to piezoelectric vibrator, piezoelectric transducer and piezoelectric drive. These devices are largely influenced by frequency temperature coefficient changing with shear angle, based on which the variation of the primary frequency temperature coefficient with around x axis and z axis rotary respectively at cutting angle θ1 and θ3 are mainly studied, and the change curve of level 1 frequency temperature coefficient with the cutting angle are drawn out at each cut. The zero temperature cutting angle of LT crystal and the approximate zero temperature cutting angle of LN crystal is then determined, which is of importance in selecting the cutting angle of the crystal device by lithium niobate and lithium tantalate.