The Technical Integration Experiment Line (TIL) prototype for Shenguang (SG) III laser facility at Research Center of Laser Fusion (RCLF) of China Academy of Engineering Physics (CAEP) has commissioned the first beam line into the diagnostic target chamber. The facility has demonstrated frequency converted Nd:glass laser energies from a single beamline of 1.43 kJ for 1.3-ns nearly flat-top pulse and 2.75 kJ for 3-ns flat-top one at 3'omega' in 2006, namely third harmonic generation (THG) efficiency of 65%-70% for two states. This paper describes comprehensive and precise theory and experiment analysis of frequency converter development and factors affecting THG efficiency for high-power laser facility.