For the heteronuclear dimer NaRb excited by a cw dye laser tuned in the wavelength region 615-645nm, 25 v'-fluorescence series, including 651 spectral lines, have been observed. Based on these lines, the molecular spectroscopic parameters of the B1 ll and X1 Σ+ states of NaRb have been determined by means of a least-squares fit. With these parameters, the potential energy functions for the B1 II and X1 Σ+ states have been calculated by the RKR method. The Franck-Condon factors and the intensity distributions of several v'-fluorescence series have been calculated. A comparison between the calculated and the observed intensity distributions has been made; the discrepancies between them are discussed.