The ultra clean 30Cr2Ni4MoV rotor steel has the advantages of high strength, good toughness and excellent performance stability, which is widely used in the manufacture of low pressure rotor and spindle of high-power steam turbine and so on. As a microalloying element, the addition of V element to the 30Cr2Ni4MoV steel will precipitate alloy carbides and refine grain, which can achieve an excellent combination of strength and toughness. However, the effect of V content on the strength and toughness as for ultra clean 30Cr2Ni4MoV rotor steel has not been reported. In this work, the effects of V content (0.1, 0.2%, mass fraction) on the carbide evolution and mechanical properties of ultra clean 30Cr2Ni4MoV rotor steel with different heat-treatment states (as tempered and as step cooled) were investigated by SEM, EBSD, XRD, TEM, and APT. The results show that both tempered steels show lath martensite microstructure. The increasing of V content has no obvious effect on the carbide type (M23C6, M2C and MC) and size, but promotes the precipitation of more and finer V-riched carbides MC, which refines the prior austenite grain size of the 0.2V steel. The refinement of grain size and precipitation of finer MC carbides increase the yield strength of the 0.2 V steel by 147 MPa through grain refining strengthening and precipitation strengthening, respectively. After step cooling heat-treatment, the microstructures and the type of carbides in two experimental steels remain stable and the size of carbide grows slightly. After the step cooling heat-treatment, the yield strength of both steels show a slight decrease due to the carbide coarsening. As for 0.2V steel, the mobility of dislocations decreases due to precipitation of more MC carbides, which induces the decrease of the critical stress σf of crack propagation promotes the tendency of crack initiation and propagation. Therefore, as compared with 0.1V steel the FATT of 0.2V steel increases by 21°C.