In this paper, we proposed a modified vacuum directional solidification system for producing multicrystalline silicon (mc-Si). A transient numerical model was carried out to simulate the process of mc-Si vacuum directional solidification which cannot be directly monitored. The temperature distribution, melt convection, melt-crystal (m/c) interface and thermal stress have been simulated. Simulation results show that the modified system is particularly suitable for growing high-quality crystal of mc-Si. The thermal stress of the silicon crystal decreases considerably due to the lower temperature gradient by installing a conical insulation unit, the m/c interface keeps slightly convex and the melt flow along the axis direction is relatively stronger by improving the heat transfer. The results of the experiment show that this modified system of mc-Si can obtain better crystal quality than the traditional vacuum directional solidification system. (C) 2014 Elsevier B.V. All rights reserved.