Abstract: Code validations are performed by comparing the calculated results against the measured data from three types of operating reactors. A total of 59 reactor cycles are evaluated and the results compared not only include the parameters measured at the startup physics test stage for zero- and low-power conditions but also that measured at the normal operation stage for full-power conditions. Validation results demonstrate that the neutronic models incorporated in ORIENT system are of high quality and the system is highly acceptable for performing routine neutronic analyses at PWR nuclear power plants.