The invention discloses a fault early warning method of a large semi-direct drive unit gearbox cooling system. The method comprises the steps that (1) SCADA data of a wind power plant are collected, and the sampling periods of label points of the data should keep consistent; (2) temperature values corresponding to the N label points in the data are extracted; (3) an actual power set value corresponding to the temperature value of each label point is calculated; (4) the actual power set value corresponding to each time point within the sampling period is compared with a threshold value, if theactual power set value exceeds the threshold value, it is reported that the gearbox cooling system breaks down abnormally, and if the actual power set value does not exceed the threshold value, it isjudged that the state of the gearbox cooling system is normal; and (5) after it is reported that the gearbox cooling system breaks down abnormally, field staff are guided to carry out troubleshootingaccording to the abnormal fault troubleshoot process of the gearbox cooling system, and repair is carried out according to the troubleshoot result till faults are eliminated. According to the method,the aims of pre-judging the abnormal state of the gearbox cooling system and eliminating the faults before the faults happen can be achieved.