Luo Huining, the former Communist Party chief for Shanxi province, has been appointed to head China's liaison office in Hong Kong, the official Xinhua News Agency said.
He replaces Wang Zhimin, who had assumed office in September 2017. Xinhua did not give a reason for the change.
The protests, which began in early June, have turned violent at times, with hard-line demonstrators clashing with police. The violence has eased somewhat in the past month, but sporadic clashes have continued.
A huge and largely peaceful march on New Year's Day degenerated into violence as some protesters attacked ATM machines with spray paint and hammers, smashed traffic lights and blocked downtown streets with paving stones ripped from sidewalks.
Police used pepper spray, tear gas and a water cannon to drive off the demonstrators, although a government statement said officers were "deploying the minimum necessary force."
The protesters are demanding fully democratic elections for Hong Kong's leader and legislature and an investigation into police use of force to suppress their demonstrations.