PSD is a very important parameter in communication. It should be measured in all the phase during communication. Since products are developed at the same time

many spectrum analyzers are needed

which will increases the cost. The appearance of the virtual instrument solves this problem. This paper expatiates on a way the virtual instrument designed for xDSL signal. It shows that virtual instrument has an advantage of low price and better functions. As a substitute for traditional instrument

the virtual instrument can greatly reduce the cost of development.