Due to increasingly stringent emission legislation, it is essential to find a solution of eliminating nitrogen oxides ($NO_x$) from diesel exhaust gas. Non-thermal plasma (NTP) approach has been studied for years and has shown advantages. In this study, $NO_x$ removal from simulated diesel exhaust gas by a dielectric barrier discharge needle-to-cylinder reactor under room temperature condition is presented. The dielectric barrier consists of a diesel particulate filter (DPF) putting in the discharge field. A simulation gas of $N_2$, NO and $O_2$ combined with particulate matters (PM) was used as the test gas. PM was loaded from a diffusion flame PM generator. The effect of PM and oxygen fraction in exhaust gas on $NO_x$ removal characteristics was investigated experimentally. The results showed that PM promoted $NO_x$ removal reactions in the barrier discharge field but its effect was dropped following elapsed time. In addition, for PM composition, soluble organic fractions and sulphate were decreased with $NO_x$ removal. Besides, the chemical reaction mechanism inside reactor was discussed.