Technology of passive location has broad prospects for application. The single observer-passive location method of phase difference rate of change is introduced based on existing methods. We can obtain the direction of the target with phase difference information of two orthogonal interferometers on the observer and the radial distance with corresponding phase difference rate of change information. Then the target can be located with high speed and precision. Some locating expressions are given when the observer is flying along a horizontal beeline without any posture change. Simulations show that this method is effective.