In order to estimate the motion parameters of the target before it passes by the CPA (closest point of approach) in the application of the LOFAR (low-frequency acquisition and ranging) sonobuoy, an unbiased estimation method is proposed, which can estimate the motion parameters of the single target using the amplitude and frequency of its radiated noise. For deriving the theoretical formulas for the parameters like the characteristic frequency, absolute speed, CPA and radiated noise amplitude, three measurements of amplitude and frequency that are evenly spaced in the range are used. With consideration to the characteristics of the practical application of LOFAR, the least squares estimation theory was used to enhance the accuracy of the target parameter estimation. The computer simulation results indicate that this method is an unbiased estimation algorithm in theory and the air experiment demonstrates the practicability and effectiveness of this method for use in engineering practice.