Due to the huge application potential and great strategic significance of low earth orbit (LEO) satellite communications, many countries are seizing the orbit resources of LEO satellites and satellite communications spectrum resources. The world has entered the area of satellite Internet Race. Aiming at the fast synchronization problem of low-orbit satellite receivers with large frequency deviation and low signal-to-noise ratio (SNR), the fast acquisition speed and large frequency offset signals input digital phase locked loop proposed in this paper can be applied well in low-orbit satellite communications.