The discrete polynomial-phase transform (DPT) method estimate chirp rate and central frequency of LFM signal based on sequential estimation of polynomial phase parameters. DPT method which has been developed by an iterative approach as Improved DPT method uses nonlinear least squares (NLS) technique to estimate phase parameters of the LFM signal. NLS have high computational load. In order to promote the precision of estimation and reduce the computational load in Improved DPT method, combined technique is proposed and used which provides an initial estimation of frequency interval based on NLS criterion in single-exponential mode and using random basis functions method.