Atomic potassium is ionized by three channels when it is excited by a pulse dye laser. They are energy pooling induced ionization, 4S→6S and 4S→4D two photon resonant three photon ionization. The ionization current intensity at various vapor temperature and laser intensity were investigated for the former two ionization channels. The atomic radiation trapping and nonlinear ionization were found in ionization current spectra. The qualitative explanations for above phenomena are given.