There exist a contest of the stealth weapons in the future battlefields, and the manned plane or the unmanned plane, cruise missile or trajectory missile are all developing in the direction of stealth, which makes it difficult for the traditional radar to detect them. In this paper, the passive quantum radar was presented which integrated the quantum technique and passive radar, and its mechanism of stealth target detection was analyzed. Microwave signal was quantized by using the superconducting circuit technique and high sensitivity of the receiver was realized by taking full advantage of advanced methods, including SVI and PSA of quantum enhanced processing at receiver, as well as JPA technique. By using passive quantum radar, the system sensitivity had been improved almost by 4 order in comparison with that of the tradition radar. The analyzed results show that the proposed method of target detection based on passive quantum radar is feasible, and it has good applicable potential.