NaNbO3 fibre catalyst can efficiently hydrogenate azobenzene to hydrazobenzene with 100 % selectivity under Xe light irradiation. The catalytic activity was closely dependent on the trans-cis photoisomerisation of azobenzene and the subsequent moderate activation of cis NN bond on Nb site. The adsorption of azobenzene with cis or trans conformation on the Nb active site was investigated by the computational methods. The apparent increase of the cis NN bond length from 1.254 to 1.348 Å, suggested an effective activation. The important role of the cis isomer in the reaction was also reflected in the quenching experiment, in which a silver quencher was used to inhibit the generation of the cis isomer. The weak interaction between Nb site and NN of hydrazobenzene was the key to inhibit the over reduction, which was confirmed by the in situ diffuse-reflectance IR spectra.