The present invention provides a plasma processing apparatus. The apparatus includes a vacuum chamber, a plasma reactor arranged in the vacuum chamber for plasma processing, an RF power source for providing RF signals to the plasma reactor and an RF power transmission unit for transmitting RF signals from the RF power source to the plasma reactor inside the vacuum chamber. The RF power transmission unit includes a transmission line for transmitting RF signals and an outer conductor for shielding the electromagnetic field around the transmission line. The invention can effectively avoid the problem of electric discharge when RF signals transmit in a vacuum chamber, resulting in more security and less transmission power loss.