The biological competition (Lotka-Volterra) mathematic model is employed to establish the bio-inhibition system; the population succession of Nitrate Reducing Bacteria (NRB) and Sulfate Reducing Bacteria (SRB) under the oil reservoir conditions is taken as the research subject, the competitive ecology relation of these two microflora is studied. The equilibrium point solution is used to explore the microflora population variations of NRB and SRB on the condition that the artificial addition of nitrate was adopted as an electron acceptor. Based on the Lotka-Volterra model, the steady-state bio-inhibition system is established between NRB and SRB. In the meantime, when the nitrate is depleted, the bio-inhibition system is collapse and finally breakdown is explained quite well by the model. According to the two critical points of NRB-SRB microflora bio-system, the precise steady-state inhibition period and the nitrate concentration under the condition of oil reservoir are able to be calculated and controlled. The results could greatly improve NRB-SRB bio-inhibition technology and accurately direct the implementation of practical process in the oilfield, which has great significance in the crude oil production.