Phase formation, thermal hysteresis and magnetocaloric effect in Mn1.25Fe0.75P1-xSix (x=0.50, 0.52, 0.54, 0.56, 0.58, 0.60) alloys have been investigated. X-ray diffraction analysis shows that the alloys crystallize in the Fe2P-type hexagonal structure (space group ) with second phase of FeSi or Fe3Si. By adjusting the content ratio of Si to P, Curie temperature increases linearly from 240 K to 313 K with the increasing of Si content, and the thermal hysteresis of the alloys decreases gradually. When the Si content is 0.58, the maximum value of the magnetic entropy change of the alloy is 8.6 J/kg·K for a field change from 0 to 1.5 T