The forging of crusher main shaft, with diameter of φ1540mm and weight of 47780Kg, requires 90 tons of steel ingot, and have a higher demand for grain size. In order to meet the demand of ultrasonic examination, some effective measures, including LF refining, VCD treatment and ingot casting in vacuum, were taken in process in smelting and ingot casting. In this paper, two main shafts were manufactured, and two technologies were adopted respectively to control grain size. One was without modification, relying on subsequent heat treatment to refine grain. The other was modification, adding a trace amount of Nb to refine grain. Both of methods finally make grain size to reach 7-8 degree, higher than the standards, achieving very good results.