Abstract: The interrupt mechanism of Windows was discussed in this paper,and a real-time clock with higher priority than the system clock interrupt was designed by using the interrupt priority mechanism in Windows.Tests and analysis results show that the new clock system is able to provide a hard real-time clock with minimum accuracy of 100 μs under the condition that no other interrupts happen.Finally,a design based on the new clock system to improve the real-time performance of Windows is put forward.