Frequency modulation continuous wave (FMCW) Laser radar (Ladar) signals inevitably suffer from nonlinear frequency modulation errors which reduce the quality of Ladar imaging. We propose a time-frequency domain nonlinear phase compensation method based on synchro-squeezing wavelet transform (SST). We first obtain the time-frequency information of the dechirp signal containing a reference range using SST. A nonlinearity model in time-frequency domain is then proposed to estimate the nonlinear phase of the transmitted signals by using the time-frequency information of the reference signal. Finally, the nonlinearity of the dechirp signal is compensated by using the estimated nonlinear phase of the transmitted signals. Numerical tests verify that the proposed method has an advantage of compensating for the nonlinear phase of noisy and multicomponent FMCW Ladar signals.