A novel low complexity time-of arrival (TOA) estimation method is presented in this paper. This method achieves a precise TOA estimation under low SNR condition for unknown intra-pulse modulated signal, especially for frequency modulated pulse. Firstly, delayed conjugate multiplication is employed to reduce the intra-pulse modulation as well as estimate the rough range of received pulse. Then, in the precise estimation part, a novel intra-pulse correlation accumulation method is used by accumulating the pre-processed signal with a proper gain. Finally, simulation results are given to examine the estimating performance and a better estimation of unknown intra-pulse modulated signal is achieved compared with the existing methods.