As potential candidate for next-generation nanoelectronic circuits, Quantum-dot cellular automata (QCA) has attracted tremendous interests among researchers. QCA circuits represent logic levels based on charge polarity inside QCA cells, which is totally different from traditional CMOS logic. It has advantages of extremely small size, high device density, fast speed and low energy consumption. In this paper, the design and simulation of a four-bit QCA BCD (Binary-Coded Decimal) full adder is reported. The four-bit QCA BCD full adder is designed and simulated using QCADesigner software. A traditional microelectronic 4-digit QCA full adder is also designed and simulated using Xilinx software. The simulation waveform is compared with the simulation results in QCA full adder to verify its function.