Abstract：Rock is the research object of petrology; nevertheless, if specific rock samples are not sufficient，petrologic research is impossible. In the in-depth study of the petrology，the mere dependence on rock samples obtained from the surface is not enough. The rock samples collected from deep earth are necessary, and the acquisition of such samples can only rely on drilling engineering. Scientific drilling can obtain the rock samples from deep earth, and researches can be carried out on the cores which carry a lot of information concerning the deep earth，and this will surely promote the development of petrology. At the same time，the research results of petrology can provide the basis for the design of drilling engineering. In addition，the in-depth study of the petrology can promote the development of the drilling technology due to its special requirement for drilling cores. Without technical support, the progress of science is impossible. Only by paying full attention to drilling engineering can importance be truly attached to geological study and to the research on petrology.