Forced convection of melt in a crucible caused by crystal and/or crucible rotation in a Czochralski crystal growth system is investigated. The dimensionless Navier-Stokes equations governing the fluid motion are computationally solved by the relaxation method. Flow patterns obtained are classified by various combinations of crystal and crucible rotation rates. Radial flow predominates near the crystal with axial flow occurring mainly in the region between the crystal and crucible bottom. If the crystal rotation rate is larger (smaller) than the crucible rotation rate, the fluid near the crystal flows upward (downward). Stagnation surfaces which prevent complete mixing of the liquid are clearly shown in flow patterns. Finally, the circulation time of the fluid is calculated.