Based on Sellmeier equations for MgO:LiNbO3(Mg:LN) crystal, the phase-matched condition and acceptance angle for sum-frequency generation of a radiation at wavelengths of 1079.5 nm and 1341.4 nm have been calculated. The calculated results were verified by the sum-frequency generation in MgO:LiNbO3 crystal with a 1079.5 nm and 1341.4 nm dual wavelength Nd:YAlO3 (Nd:YAP) CW laser. A CW coherent orange radiation at wavelength of 598.1 nm has been achieved. The possibility to obtain the 588.7 nm coherent orange radiation using a 1064 nm and 1318 nm dual wavelength Nd:YAG laser in MgO:LiNbO3 crystal was also discussed.