As part of the LSST project, a comprehensive CCD emulator that operates three CCDs simultaneously has been developed for testing multichannel readout electronics. Based on an Altera Cyclone V FPGA for timing and control, the emulator generates 48 channels of simulated video waveform in response to appropriate sequencing of parallel and serial clocks. Two 256Mb serial memory chips are adopted for storage of arbitrary grayscale images. The arbitrary image or fixed pattern image can be generated from the emulator in triple as three real CCDs perform, for qualifying and testing the LSST 3-stripe Science Raft Electronics Board (REB) simultaneously. Using the method of comparator threshold scanning, all 24 parallel clocks and 24 serial clocks from the REB are qualified for sequence, duration and level before the video signal is generated. In addition, 66 channels of input bias and voltages are sampled through the multi-channel ADC to verify that correct values are applied to the CCD. In addition, either a Gigabit Ethernet connector or USB bus can be used to control and read back from the emulator board. A user-friendly PC software package has been developed for controlling and communicating with the emulator.