Spin-locking o f central transition in half-integer quadrupolar systems was studied. The particles which occupy the states of |-1/2> and |l/2> may form an isolated sub-system, and it obeys the spin temperature theory in rotating frame. We calculated the intensity of spin-locking signal by density operator approach. The result was verified by experimental observations on 23Na-NMR spectra of NaNo2 and NaOH powders.