The laser-induced photo-acoustic (PA) spectrum of NO molecule in the wavelength region of 420.0～470.0 nm is collected with an optical parametric generator and amplifier pumped by an Nd:YAG laser as excitation source. The spectrum is composed of regular progression that comes from the excitation of X2Π(v″=0)→A2Σ(v′=0,1) and X2Π(v″=0)→E2Σ(v′=2,3,4), F2Σ(v′=1,2,3), R2Σ(v′=0,1). The variation of PA signal versus laser intensity indicates that these transitions are realized via two- or three-photon process. The signal corresponding to the two-photon process is stronger than that of three-photon process. So the optimum excitation wavelengths are 452.4 nm or 429.6 nm to detect NO with the technique of PA and with visible light as excitation source. Based on experimental data, the vibration constants of NO A2Σ, E2Σ, F2Σ and R2Σ excited electronic states are calculated from the wavelength of the spectral peaks. They are 2346 cm-1, 2342 cm-1, 2397 cm-1 and 2381 cm-1 respectively, and agree well with results by other methods.