PPP-RTK technology is gradually mature and widely used in intelligent driving, intelligent agriculture, mobile inspection, and other fields in recent years.Usually, to acquire accurate position, users must spend tens of thousands of Yuan to buy professional receiver and antenna. In contrast, the low-cost equipment is cheap but the acquired GNSS measurements from it often suffer from low signal-to-noise, high level multipath et al. When users use it to for positioning, it usually takes much time to converge to centimeter level. In this paper, we use two low-grade mass-market devices and one cheap double frequency antenna to conduct PPP-RTK experiments. During the tests, the Qianxun SI self-developed multi-GNSS SSR correction service is also used to accelerate the convergence. The result shows that it only takes several seconds to fixed for first time. Once fixed, the PPP-RTK can achieve and maintain centimeter level. It is proved that it is possible for users to acquire instantaneous centimeter-level positioning based on mass-market devices.