Nanoscale co-precipitation strengthening in steels has attracted increasing attention in recent years and has become a new cornerstone for the development of advanced high performance steels with superior combination of strength and ductility. Rolling process, finishing temperature, cooling rate and coiling temperature are the main factors which affect the mechanical properties of microalloyed steels by changing the volume fraction and particle size of precipitates. Nevertheless, the influence of cooling rate on microstructure evolution, precipitates and mechanical properties of complex microalloyed ferritic Ti-V-Mo steel has been rarely reported. In this work, the precipitation law of (Ti, V, Mo)C carbides at different cooling rates and its effect on microstructue evolution and mechanical properties of Ti-V-Mo complex miroalloyed steel were studied by OM, EBSD, HRTEM and Vickers-hardness test. The results indicated that the hardness first increased quickly and then increased slowly as the cooling rate increased (lower than 20 ℃/s); the mean size of (Ti, V, Mo)C particles decreased from 13.2 nm to 6.9 nm and the average size of ferrite grain reduced from 5.06 μm to 2.97 μm; the hardness of Ti-V-Mo steel was improved by the means of grain refinement hardening and precipitation hardening. However, when the cooling rate increased from 20 ℃/s to 30 ℃/s, its effects on grain refinement hardening and precipitation hardening has become saturated, so the hardness was kept flat and achieved a maximum vlaue of 410 HV, and the yield strength reached as high as 1090 MPa. The hardness y of Ti-V-Mo microalloyed steel and cooling rates x accord with a exponential decay relationship: y=-229exp(-x/5)+412.