N, Fe single doped and co-doped anatase TiO2 nanoparticles were successfully prepared by coprecipitation method using TiCl4, NH4OH, Fe(NO3)3·9H2O as raw materials and polyvinyl alcohol as dispersant. The samples were characterized by TG-DSC, FTIR, XRD, FESEM, EDS, XPS, and UV–Vis to investigate the influence of doping concentration on the thermal effect, crystal structure, morphology, composition, energy band gap and photocatalytic activity of TiO2 nanoparticles. Results indicated that TiO2 nanoparticles doped with 0.15 at.% N and 0.3 at.% Fe showed the best photocatalytic activity. N, Fe co-doping had a synergistic effect: (1) The transformation inhibition of anatase to rutile phase was achieved, leading to formation of high crystallized monophasic anatase TiO2; (2) The bandgap narrowing effect was significant, increasing the light absorption range; (3) The small grain size of ~ 10 nm in diameter was obtained, resulting in effective separation of photo-induced electrons and holes.