Primary dendritic competitive growth and solute concentration distribution in directional solidification DZ125 superalloy were simulated by cellular automaton coupled with finite differential method（CA-FD）in case of a fixed temperature gradient.The results indicate that the modeling can visualize the microstructural evolution of DZ125 superalloy.A solute concentration gradient of 1%/mm from the bottom to the tip in solidified dendrite exists in mushy zone at the growth rate of 10 μm/s

meanwhile

the liquid solute concentration is decreased from 44.16% at the interface to 38.68% out of the solute diffusion layer.At the growth rate of 100 μm/s

the solute concentration gradient in solidified dendrites becomes smaller

compared with that of ones at 10 μm/s

and its interface liquid concentration makes 51.54%

which is the higher than that of 10 μm/s.The liquid concentration in the dendrites is decreased from the bottom to the top as 20%/mm in mushy zone at 100μm/s

which is well in agreement with that from theoretical analysis’s.