推导了掺5 mol% MgO的liNbO3晶体折射率温度系数的表示式.利用这些表示式可以计算293～428 K温度和0.5398～1.3414 μm波长范围内的折射率温度系度，结果表明:计算值和实验值的最大相对偏差是12%，用具有最大相对偏差的折射率温度系数的计算值，计算1.0795 μm波长的非临界相位匹配温度，其值为382.4 K，它与实验值仅差6 K.因此，本文得到的表示式，对于采用这种晶体，设计在上述波长范围内的非临界相位匹配倍数频器件是有用的.

Principal refractive indices and its thermal coefficients of LiNbO3 crystal doped with 5 mol% MgO were carefully measured at the wavelengths of 0.5397 μm, 0.6328 urn, 1.0795 μm and 1.3414 μm and the temperature of 293 K, 348 K, 389 K and 428 K in the Pervious papers[1]. On the basis of measured values and modified Sellmeier's equatins, the expressions of thermal refractive index coefficients of this kind of crystal are derived in this paper. Using these expressions, the thermal refractive index coefficients in the temperature range of 293~428 K and the wavelength range of 0.5398～1.3414 μm have been calculated. It is shown that the maximum relative deviations between the calculated and experimental values is 12%. Based on the calculated value of thermal refractive index coefficient with maximum relative deviation, the noncritical phase matching temperature for 1.0795 μm is calculated to be 382.4 K, only 6 K difference with the experimental value. The expressions are useful for design of the nonlinear optical device using this kind of crystal adopted noncritical phase matching technology.