The (2+2) four-photon ionization spectra of NO via A2∑+ (v=0) and A2∑+ (v = 1) states are assigned and (3+1) MPI spectrum via F2A (v=0), H2∑(v=0) and H 2(v=0) states is discussed. Some intensity-anomalous lines of (2+2) MPI have been observed. Based on the signal-power dependence measurement for the normal and anomalous lines, a double resonance and collision Ionization model is suggested to elucidate the intensity anomaly.