Effectiveness of coker gas oil (CGO) used as industrial hydrogen donors in the visbreaking was revealed. Hydrogen-transferring abilities of different CGO narrow fractions were first analyzed. The fraction of 350–420°C (HDII) turned out to be the best selection as hydrogen donors and then we did visbreaking experimental tests. The results show that, in contrast with conventional visbreaking, the addition of HDII achieves higher conversion of residues to desirable liquid product and effectively suppresses coke formation: the coke induction period is prolonged from 17 to 27 min and the liquid-coke particle size decreases from 0.307 to 0.186 μm. The hydrogen shuttle between asphaltene and hydrogen donors is of great significance during this thermal processing.