The invention relates to a porous organic polymer catalyst and a preparation method thereof, as well as application of porous organic polymer catalyst in epoxidation of olefin. The porous organic polymer catalyst consists of Salen-Mn ligand and 1, 3, 5-acetylenyl benzene, is prepared through Sonogashira-Hagihara coupled reaction, has the advantage of being simple to prepare, and can catalyze the olefin to react with oxygen and isobutyraldehyde to generate epoxidation reaction with relatively high activity and relatively high selectivity. The catalyst can be simply separated from a product, and can be repeatedly used for many times.