In this paper, Co ₃O ₄、MoO ₃and Se powders were used as precursors in in-situ co-growth chemical vapor deposition method. Cobalt-doped MoSe ₂nanosheets were grown on SiO ₂substrate at 710 ℃. The influence of hydrogen content on its growth and regulation mechanism was discussed. Surface morphology analysis showed that the introduction of hydrogen promoted the formation of oxy-selenium metal compounds required for nucleation and the CoMoSe compound molecules required for lateral growth. AFM(atomic force microscope) results show that hydrogen is beneficial to the growth of single-layer two-dimensional cobalt-doped MoSe ₂. With the increase of the amount of Co ₃O ₄precursor, the Raman and PL(photoluminescence) spectra of the sample showed red shift and blue shift, respectively, and the bandgap was modulated from 1.52 eV to 1.57 eV. The XPS(X-ray photoelectron spectroscopy) results analysis showed that the elemental composition ratio of Co was 4.4%. The magneto and electric properties of the samples were analyzed by SQUID-VSM(superconducting quantum interference device) and semiconductor parameter analyzer for electrical testing. The results show that MoSe ₂changes from diamagnetic to soft magnetic after Co incorporation; the threshold voltage of back gate FETs is shifted by 5 V from pure MoSe ₂, and the off-state current is lower. This research provides a basis for the research and application development of ultra-thin two-dimensional materials.