CN radical plays an important role in the process of life formation. The generation of CN is closely related to nitrogen(N2) and methane(CH4) in the early planetary atmosphere. Considering the atmospheric compositions of Titan, N2 and CH4 are mixed to simulate the early atmospheric environment, then the simulated atmosphere is discharged to generate CN. The influence of CH4 to N2 ratio and the trace gases in Titan atmosphere on the generation of CN are studied by measuring the absorption spectrum of CN radicals. It is shown that, under the low-pressure glow discharge of N2 and CH4 mixture, the concentration of CN radicals is the largest when the CH4 gas pressure accounts for about 20% of the total gas pressure. When the pressure ratio of N2 and CH4 is kept constant, the concentration of CN radicals increases with the increase of total pressure at first. When the total pressure reaches 60 Pa, the concentration of CN radicals will slow down with the increase of total pressure, and when the total pressure is more than 90 Pa, the concentration of CN radicals starts to decrease slowly with the increase of total pressure. Given the gas pressure and the CH4 to N2 concentration ratio, the concentration of CN radicals increases with the increase of discharge current. It is well known that there are trace amounts of water vapor (H2O), carbon dioxide (CO2) and carbon monoxide (CO) in Titan atmosphere, and it is found that the addition of a small amount of these gases in the discharge of N2 and CH4 mixture will suppress the formation of CN radicals.