As research in the field of the photoelectron and electromagnetic wave s continues,the development of terahertz wave has attracted more and more attent ion.This paper proposes a new and potential structure of the tunable and narrow-band terahertz wave (THz-wave) radiation via the nonlinear optical diff erence frequency generation on a periodically poled Mg-doped lithium niobate(PPMgLN) crystal. According to quasi-phase-matching (QPM) in the PPLN crystal based on the theoretical model of three wave interactions in a nonlinear medium and the output characteristics of dual-wavel ength erbium-doped fiber laser,the experimental refractive index difference on the periodically po led Mg-doped lithium niobate crystal is given.Through analyzing the working temperature and t he grat ing period on its output of the THz-wave in theory,the reliable method to generate the conti nuous-tunable output wave through the PPMgLN in a small frequency range is obtained.The DFG device s tructure is relatively simple,low cost,and the tuning is easy to implement.In addition,the l aser can be operated at room temperature.