The positioning accuracy of multilateration will be directly affected by the estimation error of time of arrival （TOA） of the preamble pulse signal. First， on the basis of the mathematical model of the differential matched filter（DMF）， the relationship between TOA accuracy and sampling frequency is analyzed. And the time structure relationship between non ideal pulse signals is discussed. Then the modified algorithm is presented， which is used for TOA timestamp marked by zero crossing with four-pulse preamble DMF. The results show that the root mean square error （RMSE） is changed with SNR， sampling frequency， complexity and other parameters， and the TOA accuracy of four-pulse signal detection is higher than that of single pulse and dual-pulse signal detection. Moreover， the TOA accuracy of matched filter and DMF are compared， and results show that the DMF algorithm is more effective. When the sampling frequency is 40 MHz the SNR is 40 dB， the TOA accuracy of the four-pulse signal DMF is 0.402 7 μs， which is far less than the maximum time error accuracy of 25 μs specified by International Civil Aviation Organization （ICAO）. Finally， the real operation data are used to verify the accuracy improvement of TOA estimation and the availability of the algorithm.