Gradient metasurfaces are extensively utilized for polarized beam splitting (BS) in classical and quantum optics. Specifically, their phase gradient allows the path and polarization of multiple output lights to be locked by corresponding inputs. However, the full potential of this unique path-polarization-locked property in multi-beam splitting has not been investigated. Here, we demonstrate that a single metasurface can function as sequentially linked beam splitters, enabling the parallelization of a series of BS processes, which provides a multi-beam interference capability. In the classical region, we demonstrate that parallel BS allows continuous modulation of output light intensity and polarization state through input polarization adjustment. While in the quantum realm, parallel BS introduces an additional path-polarization correlation into Hong-Ou-Mandel interference for orthogonal circularly polarized photons. The principle of parallel BS through the metasurface presents a versatile approach to manipulate light at the micro-scale, which will have potential applications in optical computing and on-chip quantum information processing.