The diets of calves are predominantly milk, and the beginning of solid feed intake triggers a critical process of the activity of the rumen microbiota and ruminal fermentation. However, little in know about the rumen bacterial diversity changes in dairy bull calves induced by milk replacer and other starters such as solid pellets or hay. The effects of replacing part milk replacer with pellet diet and Chinese wildrye in the diet on growth performance and rumen bacterial composition of dairy bull calves were analyzed. Thirty-two newborn Holstein bull calves with initial weight of (42 ± 5) kg were randomly allocated to 4 dietary treatments: Group MFC were fed milk replacer, pellet diet and Chinese wildrye, group MFR were fed milk replacer and Chinese wildrye, group MCO were fed milk replacer and pellet diet, group MIL were fed milk replacer only. One week for pretrial and 7 weeks for experiment. At the end of the experiment, 3 calves from each treatment were slaughtered to determine the growth performance and slaughter traits, and rumen bacteria composition were analyzed by using 16S rRNA gene sequencing. Results showed that body weight, withers height, body length and heart girth were higher (P < 0.05) in MCO and MFC group compared with those in MIL and MFR group. Besides, fresh weight of liver, spleen, lung, kidney, rumen, reticulum and abomasum were also higher (P < 0.05) in MCO and MFC group. Sequencing results showed that both at phylum and genus level, group MIL and MFR cluster together, while group MCO and MFC cluster together. Bacteroidetes and Proteobacteria showed higher abundance in MIL and MFR groups, and Firmicutes showed higher abundance in MFC and MCO groups. The abundance of genera such as Dialister, Acidaminococcus and Mitsuokella were higher (P < 0.05) in the MCO and MFC group. Our results showed that the growth performance of calves could be increased by feeding milk replacer with pellet diet and Chinese wildrye, and also indicated that this may associate with changes of the rumen bacterial diversity or abundance, especially bacteria from the phylum Firmicutes.