Abstract: The geomagnetic daily variations of the vertical component, which were recorded by a geomagnetic network in Jiangsu province, are investigated with the method of Multitchannel Wiener Filtering. The results show that the daily standard errors between raw data and the actual output of the filter for the nearest station from the epicenter are distinctly higher than the ordinary level before (especially three days before) the Huanghai earthquake, then return to normal level after the earthquake.