The present research employs in-situ plasma Optical Emission Spectroscopy (OES) to explore the effect of microwave plasma jet chemical vapor deposition (MPJCVD) on activating CH₄+H₂ plasma environment and synthesizing diamond film. Surface morphology and main orientation of lattice plane of the diamond synthesized under different processing parameters are also examined. Since species such as CH, H₂, hydrogen Balmer alpha (H_α), carbon dimer (C₂) and hydrogen Balmer beta H_β in the plasma radical are easily influenced by gas concentration, substrate temperature and processing parameters, in-situ OES is employed to diagnose in-situ OES diagnosing is employed to composition of plasma species in the synthesis of diamond film. Our findings reveal that species such as CH, C₂ and H_β in microwave plasma jet have significant influence on grain size, surface morphology and H/C carbon concentration. The Raman spectrum measurement can prove the relationship between CH/C₂ species density and diamond surface morphology.