Abstract: The oscillation of the three-order functional differential equation was further studied，and some lemmas of the oscillatory solution of the differential equation were given by the operator and the integral technique. By means of these lemmas，some results in the recent literature were extended and improved，and a sufficient condition for the oscillation of solutions of the three- order functional differential equations was given. The results fully reflected the effect of time delay on vibration of equations.

Key words: three-order functional, oscillation, differential equations