Aiming to overcome the disadvantages of small molecule photosensitizers, a novel macromolecular photosensitizer was designed and synthesized in this work. Firstly, the functional small molecule photosensitizer 9-oxo-9H-thioxanthene-2-carboxylic acid (TX-COOH) and precursor poly(2-hydroxyethyl methacrylate) (PHEMA) was individually synthesized. Then, the macromolecular photosensitizer PHEMA-TX was realized by an optimized reaction procedure between PHEMA and TX-COCl, which was previously prepared by acyl chlorination of TX-COOH. The modification efficiency was calculated as 64%. Finally, the photocatalytic reaction using the as-synthesized PHEMA-TX was investigated based on three substrates of tris(4-methoxyphenyl)phosphane, methyl (phenyl)sulfane, (4-methoxyphenyl)boronic acid. The results showed that the photocatalyst PHEMA-TX can be easily separated, recovered by a simple precipitation, and reused 7 times without significant loss of the catalytic activity. The excellent photocatalytic property, easy separation, and recyclability of PHEMA-TX were comprehensively confirmed, which contributed great potential of this novel macromolecular photosensitizer in future application.