With the wide application of power electronic devices in power systems, the demand for small time-step (≤ 2μs) electromagnetic transient real-time simulation increases. While a CPU is unable to meet the demand alone, there is a trend to complement it with a Field Programmable Gate Array (FPGA). A CPU-FPGA heterogeneous computing platform available for real-time simulation of virtual synchronous grid-connected inverter system is built. Within it, the circuit part on the FPGA is implemented with an optimized Electro-Magnetic Transient Program (EMTP) algorithm. Constant admittance switch modeling, branch division with parallel processing and high efficiency matrix operation are used to improve real-time performance. The control part on the CPU adopts virtual synchronization control and designs a data interaction interface for asynchronous communication with the FPGA. A small step real-time simulation of the grid-connected inverter system is conducted and compared with the results of a Simulink offline simulation. At the same time, the real-time performance of the platform and resource consumption on FPGA is analyzed. All results above can verify the accuracy and effectiveness of a real-time simulation of the virtual synchronous grid-connected inverter system based on the proposed platform. This work is supported by National Natural Science Foundation of China (No. 51877133).