We have measured the resonant ionization spectrum of alkali-metal potassium vapor in the range of 5780 A - 5920 A, using a flashlamp pumped tunable dye laser. The results show that the two-photon transitions of atomic potassium 4s-ns (n=12-18), 4s-nd(n=10-16) and stronger atomic potassium 4p-7s, 4p-5d transitions have been obtained. These ionization signals of 4p-7s, 4p-5d transitions are produced from potassium dimer-potassium atom hybrid two-photo transitions. We have discussed the results.