Abstract: Selection of deformation parameters is very important in numerical computation and stability evaluation of the jointed rock masses engineering.When in-situ tests cant be made,an empirical method has to be used to estimate parameters to be used in simulation.This paper presents an improved empirical method for determination of deformation modulus for jointed rock masses based on many existing empirical methods commonly used in the world including size effect reduction and jointed character reduction of the intact rock specimen.Three case studies for dam sites and hydropower plants are presented as examples in the paper.