In order to improve the removal efficiency of nitrogen pollutants in traditional heavy oil processing waste water treatment plants and achieve synergistic removal of carbon and nitrogen pollutants, based on the operation parameters of the biochemical device on site and the previous research results, a pilot test device and operation parameters in a two-step-feeding anoxic/oxic (A/O) process was constructed in this paper. The side-line experiment was carried out in a heavy oil processing wastewater treatment plant with the effluent of the hydrolysis acidification unit as the treatment target. Control process conditions, the ratio of step-feed influent water is 7:3, the reflux ratio of external circulation is 1, dissolved oxygen concentration (0.1~0.4 mg/L in the anoxic zone, 3.5~4.5 mg/L in the aerobic zone), pay more attention to the effects of the reflux ratio R of internal circulation of the first-stage A/O and the amount of additional carbon source (glucose) in the denitrification stage of the second-stage A/O on the removal efficiency of nitrogen pollutants. The results show that a proper increase of the reflux ratio in internal circulation and the carbon source addition can significantly improve the total nitrogen removal capacity of the two-step-feeding A/O process and will not reduce the removal efficiency of organic pollutants. The optimum reflux ratio R value of internal recycling is 0.5, and carbon source addition is 30 mg/L, under which the removal rate of total nitrogen can reach 84.7%, and the total nitrogen mass concentration of effluent can be controlled below 10 mg/L, thus realizing the deep denitrification of heavy oil processing wastewater.