Abstract: The nitrogen plasmas produced by microwave are investigated and the rotational temperature is obtained by simulation of experimental spectra using the second positive bands of nitrogen molecule C3Πu-B3Πg (vibrational transition 0-2). The rotational fine structure of spectra is discussed in detail and all the possible line broadening effects are considered for the experimental spectra to explore the best fitting. The Self-Absorption line broadening effect is found to play an important role on the rotational fine structure in simulation than other effects in low temperature weakly ionized plasmas and a new line broadening function of Self-Absorption effect is applied to simulate the rotational spectra, which will not make a great difference on estimation of rotational temperature in simulation.