This research presents a precise evaluation of the recession of monsoonal maritime glaciers at Mt. Dagu, based on multi-source remote-sensing data of an aerial topographic map from 1966 and Landsat MSS, TM, ETM+, and OLI data from 1975 to 2017 for six sub-regions of the glacier covering 1.747 +/- 0.068 km(2) at present. The results show that: first, the area of glacier exhibits an exponentially decreasing trend and retreated as much as 5.094 +/- 0.301 km(2) during 1975-2017, with a shrinkage rate of 0.120 +/- 0.004 km(2)a(-1). Second, the highest area shrinkage rates of glaciers are in the north, northwest, southwest, and south aspects. The largest retreat altitude of the glacier terminus is in the southwest aspect of region 2. Of which, the absolute retreat elevation is 303 m (from 4587 to 4890 m a.s.l.), at a mean rate of 7.2 m a(-1). Third, the temperature has increased at a rate of 0.02754 degrees C a(-1) (R-2 = 0.6132, p < 0.05) by a total of 0.9 degrees C (1961-2017), more higher than the region's average increase. However, there is no significant increasing precipitation trend. The warm-dry trend is aggravated and this is the main reason for the glacier recession. Finally, the accelerated retreat presents a severe challenge to the sustainability of the glaciers and glacier-oriented tourism. Active intervention to maintain the glacier should be urgently considered.