Net emission coefficients of radiation were calculated for isothermal plasma of CH4 –Ar as a function of the plasma temperature 5,000–30,000 K and the arc radius (0–1 cm) at various plasma pressures. Calculations take into account continuum and line radiations. The line shapes in our calculations are given by convolution of Doppler and Lorentz profiles, resulting in a simplified Voigt profile. The overlapping lines have also been taken into account. In the case of hydrogen profile, we used the Vidal tables, and the four first Lyman lines and the four first Balmer lines have been considered in this work. Values of net emission coefficients calculated for various spectral regions were compared with others author’s works.