Abstract: The effect of duty-ratio on the characteristics of high pressure DC glow discharge of CH₄/H₂ plasma was investigated by monitoring the current/voltage waveforms and diagnosis of plasma emission spectrum.The results show that the duty-ratio has a major impact.For instance, with a duty-ratio above 73% at 1.7 kHz, it took 10~20 ms (100~200 ms) of rising time for the voltage (current) to be stable.The current increased with the increasing discharge voltage in a rapid-slow manner, considerably lagging behind the voltage.As the duty-ratio decreased, the time constant increased almost linearly, because smaller duty-ratio produced lower electron density at the beginning of ascending channel.At a high pressure, as the duty-ratio decreased, the H_α and H_β emission intensities increased because the increased discharge power heated neutral particles, significantly promoting particle collision.A duty-ratio too small reduced the e-density and increased the time constant, resulting in an unstable or quenched discharge.