Abstract: Electron-Multiplying CCDs (EMCCDs) are high-speed devices to record images of dim objects. For the high-speed recording capability of an EMCCD to be actually used, it is necessary to equip a high-speed data-transmission channel in the camera incorporating the EMCCD. The USB3 Vision standard was released by the Automated Imaging Association (AIA) in early 2013 to be used for high-speed image-data transmission. The standard defines the camera behavior for working with a USB3.0 bus and the approach to use a USB3.0 interface. Based on the characteristics of EMCCDs of high-speed readouts and the USB3 Vision standard, we have designed a high-speed data-transmission system for EMCCD cameras. The paper first briefly describes the design of the system. It then mainly discusses the transmission system and the associated image-acquisition software. The system was constructed by using an old digital controller of an EMCCD camera and designing a new USB3.0 controller. The USB3.0 controller was designed within the QUARTUS II development environment using the VHDL language. The USB3.0 controller is used to generate read-write timing signals and other logic-operation signals required by the USB3014 chip, to output simulation images, and to convert the data-transmission format according to the USB3 Vision standard. The image-acquisition software is programmed with the C++ by utilizing some API (Application Programming Interface) functions provided by the CYPRESS Semiconductor Corporation. We have carried out experiments to test the transmission system after its full construction. The image-acquisition software can download the configurable firmware for the USB3014, display the device information, provide the interface for setting the ADC parameters, and capture image frames. With the software, image frames can be captured separately or in a batch, and the images within the frames can be saved automatically or manually. A measured bit error rate of the system is less than 7.28×10^-13 if the transmission line is 1.5m long and the transmission rate is less than 266MB/s. The experiments show that our system meets the requirements on the transmission speed of an EMCCD camera, and its bit error rate also fits USB communications.