Numerical simulation of three-dimensional dendritic growth is performed by using a macro-micro coupled method and a capturing liquid method. The growth of the dendritic is controlled by the solution of the phase field equation. Since it is difficult to compute the microstructure of a whole casting, a scheme is adopted that the temperature field is calculated on the whole casting while the microstructure computation is carried out by selecting a macro-cell in the casting samples. Under the condition of not changing the phase-field model, a calculating method is advanced, which captures the liquid cells into the interface ones. In that method, every calculated micro-cell is endowed with a variable which identifies whether the cell is in the interface region and the phase field equation is only solved for those cells in that region. When the grain grows, the method captures the liquid cells into the interface ones and pushes the interface regi on forward. For the captured liquid cells, the values of the phase variable are modified. We apply the calculating method to improve the calculating efficiency, so the simulation of three-dimensional single grain and multiple grains growth for aluminum alloy samples, can be processed. The simulation results are compared with those obtained experimentally.