A configuration of 3-(PRRPR)RC parallel platform was proposed to meet the dual requirements of orientation adjustment and vibration isolation. The mechanism consisted of three limbs, in which the large-stroke actuator and the passive vibration isolation unit existed in the form of closed-loop sub-chain. In the case of passive vibration isolation, it was assumed that the actuator was instantaneously locked, and the equivalent motion screw was used to describe the closed-loop sub-chain and the orientation adjustment and vibration isolation platform was instantaneously equivalent to a 3-R(RC parallel mechanism. Based on the screw algebra and QR decomposition, the first and second order influence coefficients of the mobile platform and the limb links in the passive vibration isolation mode of the orientation adjustment and vibration isolation platform were derived. Based on the dynamic model, the vibration differential equation of the platform was derived when the foundation was excited by simple harmonic motion. The vibration response was solved by the superposition method of vibration mode, and the corresponding numerical examples were given. The prototype of the orientation adjustment and vibration isolation platform was designed, the experimental system was built, and the passive vibration isolation experiments in x, y and z directions were carried out. Numerical examples and experimental results showed that the vibration transmissibility of the prototype in three directions was less than 55%, that was, more than 45% of the vibration was isolated, which verified the effectiveness of the passive vibration isolation of the designed parallel platform.