To master the underwater rock breaking characteristics of rock drill rod and clarify the rock drilling parameters of foundation trench rock treatment of deep and medium channel immersed tunnel，we apply the multi-factor orthogonal test to study the effects of lifting height，chiseling times，row spacing and bit spacing on average fragmentation，non-uniformity coefficient，fractal dimension and reef clearing thickness. The results show that the average block size is positively correlated with the lifting height，row spacing and bit spacing，and negatively correlated with the number of chisels；The non-uniformity coefficient is positively correlated with lifting height，row spacing and bit spacing，and negatively correlated with chiseling times；The fractal dimension is positively correlated with the number of chiseling，and negatively correlated with the lifting height，row spacing and bit spacing；Reef clearing thickness is positively correlated with lifting height and chiseling times，and negatively correlated with row spacing and bit spacing. Based on the results of multi-factor test and research，the on-site rock drilling parameters are set as follows. the lifting height of rock drilling rod is 27 m，the number of chisels is 3 times，the row spacing of rock drilling points is 2.5 m，the spacing is 1.7 m，thus the rock fragmentation is appropriate and reef cleaning is not difficult. Overall，good construction results are achieved.