Based on published literatures about lunar laser ranging with three retro-reflectors landed on the Moon by the astronauts of Apollo 11, 14, and 15 missions in 1969—1972 and the two retro-reflectors landed on the Soviet roving vehicles in 1970—1971, some related physical and technical problems in lunar laser ranging are analyzed and discussed. These problems include: 1) the direction of the retro-reflector array and the accurate determination of its position on the lunar surface; 2) the identification of laser echo signals from the retro-reflector; 3) the intensity of receiving signals and the signal-to-noise ratio; 4) the precision of the lunar laser ranging results; 5) the difficulty of ranging in the full moon period; 6) the effect of the Earth's atmosphere on lunar laser ranging and its precision. Some key technical details in the ranging loop have not been given in the published literature. There is a lack of direct physical evidences for the identification of signals as the laser back from retro-reflectors. The further analysis on the relationship between the lunar ranging precision claimed and the laser characteristics is needed.