An external-cavity diode laser based on an intra-cavity electro-optic modulator tuning is developed in this paper. Electro-optic crystal lithium niobate (LiNbO3), with no hysteresis effect and high response speed, is used to replace the traditional tunable part piezoelectric transducer (PZT). The linewidth of this laser at free running mode is about 133 kHz. In addition, in the ultra-narrow linewidth laser system, the error signal is fed back to the driving voltage of LiNbO3 to realize laser locking, which can avoid the problem of laser output power fluctuation caused by feeding back to the laser injection current. The self-developed crystal-tuned laser has been successfully used in an ultra-narrow linewidth laser system, and the experimental results show that the linewidth of its beat frequency signal is about 1.5 Hz.