The vertical profiles of atmospheric pressure and optical refractive index have been theoretically analyzed and formulas that express the vertical atmospheric pressure and refractive index distribution have been derived,and their simplified forms have been given.The refractive index at any height above sea level in the troposphere can be determined and the average refractive index can be calculated by the formula,so high precise distance measurement can be attained.The measuring error arising from using the ground refractive index has been analyzed.