The reason for the difference between the composite X-ray spectrum for radio-loud quasars (RLQs) versus radio-quiet quasars (RQQs) is still unclear. To study this difference, we built a new composite X-ray spectrum of RLQs using Chandra X-ray data and Sloan Digital Sky Survey optical data for the sample of 3CRR quasars. We find the X-ray spectra of all 3CRR quasars, except for 3C 351, have no soft X-ray excess and can be fitted well with an absorbed power-law model. Our composite X-ray spectrum is similar to that of Shang et al. for RLQs, showing higher hard X-ray and lower soft X-ray flux than the composite X-ray spectrum of RQQs. Most blazar-like 3CRR quasars have higher X-ray flux than the median composite X-ray spectrum, which could be related to the contribution of beamed jet emission at X-ray band. From the literature, we find that nineteen 3CRR quasars have extended X-ray emission related to radio jets, indicating the inevitable contribution of jets at X-ray band. In contrast to RQQs, the X-ray photon index of 3CRR quasars does not correlate with the Eddington ratio. Our results suggest that the jet emission at X-ray band in RLQs could be related to the difference in composite X-ray spectrum between RLQs and RQQs.