Aiming at the common carrier frequency offset phenomenon in 5G downlink systems, an improved joint frequency offset estimation method based on DMRS is proposed. Firstly, the frequency offset is roughly estimated by CP correlation in the time domain, and compensated when the frequency offset is greater than 15k Hz; Then in the frequency domain, in order to reduce the influence of channel noise and fading, the crosscorrelation between the DMRS extracted on the receiving end and the original DMRS generated locally are calculated to obtain the channel response value, and then uses the DMRS channel response values of two OFDM symbols in one slot are used for fine frequency offset estimation. The method proposed enables a higher estimation accuracy when the frequency offset is ［-15 kHz, 15 kHz］, and improves the overall performance of the system, it has been applied to a 5G multichannel base station comprehensive test instruments.