The invention discloses a quick time-frequency synchronizing method under the low signal-to-noise ratio. The method is used for time-frequency synchronization of signals between a transmitting terminal and a receiving terminal. The method specifically comprises the following steps that (1), a linear frequency modulation sequence is used as a spread spectrum sequence of a data package, wherein the cycle is N, and the cycle width is Tc; (2), the linear frequency modulation sequence of one cycle serves as a local sequence, moving correlation is carried out on the spread spectrum sequence of one cycle and the received local sequence from the beginning of time t, a first correlation peak value is obtained, and the position where the first correlation peak value occurs is tp; (3), moving correlation is carried out on the spread spectrum sequence of another cycle and the local sequence from the beginning of time (t+delta T), and a second correlation peak value is obtained; (4), the phase difference delta theta between the first correlation peak value and the second correlation peak value is solved, a frequency offset estimation value fd=delta theta/2*pi*delta T is obtained to carry out frequency offset compensation on the data package, and the frequency synchronization is finished; (5), the correlation peak value position offset nd=round(fdNTc) is calculated, the initial position of the spread spectrum sequence is tp+ndTc, and time synchronization is finished, wherein the correlation peak value position offset is caused by frequency offset.