The invention discloses a transverse prestress reinforcement method of a railway simply-supported T beam. The transverse prestress reinforcement method comprises the following steps: S1, the steel barposition of a main beam web of the railway simply-supported T beam is detected; S2, hole position drilling of a transverse prestress steel beam is conducted; S3, common steel bars are anchored; S4, the steel bars are pre-tightened; S5, the transverse prestress steel beam is mounted; S6, a formwork is mounted; S7, the transverse prestress steel beam is primarily pulled; S8, the transverse prestress steel beam is finally pulled, specifically, the transverse prestress steel beam is pulled after the concrete strength reaches 75-85%, pulling is conducted in two steps, and pulling force each time is 190-200 kN; and S9, anchor sealing is conducted, specifically, anchor sealing is conducted through C50 reinforced concrete. According to the transverse prestress reinforcement method, through a finite element analysis method of the transverse reinforcement effect of the railway simply-supported T beam, the self-vibration frequency after reinforcement can be accurately estimated, and increasing of the bridge transverse stiffness is promoted through the transverse prestress reinforcement method.