Aiming at the problem of the clock inaccuracy and the inconsistency between the data time and the actual time in relative recorders of the geomagnetic network,the paper proposes a check of the accuracy of geomagnetic data clock with the checking value by the extremum matching method during the period of geomagnetic disturbance. We checked the accuracy and reliability of the method in using geomagnetic data provided by the National Geomagnetic Network in March, 2015 of China. Experimental results show that when clock difference exceeds 1 minute error data,the detection rate runs up to 100%,and the method can give an error correction time in less than 2 minutes with the accuracy rate of 94.44%. The method provides a technical support for the monitoring of the accuracy of a large number of instruments and the data clock correction during the disturbed day.