Complex Programmable Logic Device(CPLD) and Field Programmable Gate Array(FPGA) play more and more important roles in design of modern digital system. But sometimes, the glitch in design of the system become handicap of succeedable design. This paper analyses the cause, judge and locate of glitch in design of modern digital system apply the component of CPLD/FPGA. Three methods about eliminate the glitch make use of EDA tools are discussed and some examples are given.