The populations of np forbidden transition states for two-step excitation of Na atom have been obtained by appling the static field of strength 167 V/cm. We have obtained lifetimes of np(n = 19-23) states by the method of delaying ionization in pulsed electric field, and have compared the calculation values with the measured data. The influence of applied fields and environmental radiation on the determination of the lifetimes of the highly excited states were discussed.