Based on an important project at Qingdao, vertical static load test and the pile shaft stress test were conducted on five manual hole digging and pilling piles installed into argillaceous siltstone. The load transfer mechanism and vertical load bearing capacity of the large-diameter rock-socketed piles were discussed through the measured data. The test results showed that the load-displacement of five test piles was slow type, with the pile sedimentation less than 11 mm and larger unloading resilience ranging from 51%~75%, and all the piles had high bearing capacity which could meet the design requirements. Under the ultimate load, the proportion of head load transmitted and supported by the shaft base was between 10%~20% and decreased along with the increase of the shaft length and socked length (socketed into medium weather part), which showed the characteristic of end-support friction pile. The load of the shaft gradually worked from the top to the toe, and the soil side friction reached its ultimate value at first, while the peak side friction located at the medium of the socked length. The deeper of the socked length, the more safety stock of the pile, and the measured side friction was 2.5 times of the recommendation at the medium weathering rock. The percentage of the socked part supporting the total loading increased from 39% to 45% along with the increasing applied load, and the side friction of the socked part played an important role while the end resistance possessed a quick growth ratio. Based on the standard and data of static load test, vertical bearing capacity of the manual hole digging pile was refreshed, and the pile size was optimized in order to save the materials and improve the effectiveness of the construction, leading to the great economic benefits.