Recently,Lambert W function has been found successful applications in stability analysis of time-delay systems.Because Lambert W function is defined as the solution of a transcendental equation,and it works only if some mathematical softwares such as Maple,Matlab or Mathematica are available,so the stability criteria based on Lambert W functions are not easy for understanding in applications.In this paper,two simple stability criteria have been derived from a careful investigation of the root location of Lambert W function,so that the stability as well as the robust stability of some time-delay systems checked by using Lambert W function can now be tested simply by calculating elementary functions.