The pile skin friction design parameters for the mudstone foundation are scant. According to the test data of large diameter deep piles of the Songhua River large bridge by means of the Osterberg cell pile test in Jilin Province, and in conjunction with the medium-scale shear test between the pile and mudstone, the interaction mechanism and load characteristics of mudstone skin friction were revealed, leading to some constructive conclusions for the design and in-depth research of the cast-in-place pile for mudstone foundation. The results show that: the end resistance of large diameter deep piles only accounts for a small part of the bearing capacity of the total load, so it belongs to the friction type pile. By means of the Osterberg cell pile test, skin friction in completely weathered mudstone, strongly weathered mudstone and moderately weathered mudstone reached 173kPa, 279kPa and 336kPa respectively. These values of mudstone skin friction are greater than specified reference ones. In the design of pile foundation, it is recommended that the mudstone skin friction estimated using the shear strength parameter measured by medium-scale shear tests, and based on the Mohr-Coulomb criterion, can provide economical and reliable parameters for estimating the bearing capacity of piles.