Potassium tunable ultra-narrow bandwidth optical filter at 532nm was studied theoretically and experimentally (T-ESFADOF). The theoretical model of T-ESFADOF was proposed and the transmission spectrum of T-ESFADOF was calculated. The transmission spectra under different electric fields were measured. The e xperimental frequency shift of T-ESFADOF versus electric field and the comparins on with the corresponding theoretical curve have been given