Temperature dependence functional expressions of bond length and thermal expansion coefficient of alkali halides without empirical parameters were established with local bond average approach and definition of thermal expansion coefficient. We obtained quantitatively the bond length, rigidity factor, Debye temperature and thermal expansion coefficient of alkali halides. It was found that: ① The thermal expansion coefficient of alkali halides is inversely proportional to the cohesive energy; ② The Debye temperature decreases and the thermal expansion coefficient increases gradually from alkali fluorides to alkali iodides in the same kind of alkali halides; ③ The bond length of alkali halides changes from nonlinear to linear thermal elongation at one third of its Debye temperature.