The test 600 MPa grade high strength steel (/% : 0.23C
0.67Si
1.35Mn
0.028P
0.023S
0.131V
0.033Nb) is melted by a 25 kg vacuum induction furnace and hot-rolled to 16 mm x 180 mm slab product. With dilatometric test combined with structure metalloscopy and microhardness test the continuous cooling transformation expansion curves of steel HRB600 at cooling rate 0.1-100 ℃/s have been measured by hot simulation testing machine Thermecmastor-Z to got the continuous cooling transformation (CCT) curves of the steel and the transformed structure of steel is studied. Results show that with austenizing at 850 ℃,as cooling rate less than 3 °C/s the structure of tested V-Nb microalloying high strength steel HRB600 is proeutecloid ferrite + pearlite; with cooling rate 5 ℃/s the minor martensite occurs in structure to effect the welding behavior of steel ; and with cooling rate up to 100 ℃/s the martensite structure is obtained in steel.