The nickel-based superalloy is among the most important high-temperature structural materials, of which the casting microstructure and especially the dendrite structure can affect the final performance of the superalloy parts. In this work, the phase-field model was coupled with thermodynamic database to simulate the dendrite growth in the multicomponent nickel-based superalloy solidification. And the GPU device was used to accelerate the computation and large-scale phase-field simulations were achieved. The single-crystal dendrite growth was simulated, and the results exhibit a transient and stable growth stages during the formation of primary dendrite arms. The dendrite competitive growth in bicrystal directional solidification (θ=±15°) was also investigated. And the favorable oriented dendrites were able to overgrow the unfavorable oriented dendrites in diverging grain boundary. While the grain boundary remains unchanged in the converging dendrite growth simulation. At last, the effects of natural convection on dendrite growth were investigated, and the simulated microsegregation pattern of the alloy components agreed well with the experimental results.