Ni(Nickel)-based superalloys are used as indispensable materials for turbine blades in aero-engines because of their excellent creep, fatigue and corrosion resistance. Co(Cobalt), as one of the new key elements in Ni-based superalloys, has attracted extensive attention in Ni-based superalloys field. However, the effect mechanism of Co on Ni-based superalloys is still controversial. To solve this problem, tensile properties and microstructure of Ni-based superalloys doped with or without Co (5 %) have been investigated through molecular dynamics simulation, and the joint impact of temperature and Co on the superalloy mechanical properties has also been analyzed. The findings indicate that 5 % Co doping reduces the yield stress, yield strain, and elastic modulus of the structure, while increasing the flow stress at 300 K–600 K; however, the advantage decreases at 900 K and disappears completely at 1200 K. This can be explained that Co doping leads to more slippage of stacking faults in the elastic stage and hinders the loop formation of dislocations at 300 K–600 K, while more Stair-rod dislocations occur in the plastic stage. These effects disappear at 900 K–1200 K. •The effects of Co and temperature on mechanical properties of nickel-based superalloys were studied by molecular dynamics.•The combined effect of Co and low temperature results in more stationary Stair-rod dislocations, resulting in increased flow stress.•Co leads to more HCP and stacking faults in γ' phase, hinders the formation of dislocation loops and decreases tensile strength at 300 K-600 K.