The Virtual Sound Intensity Analyzer is a new instrument which has more advantages than the traditional Sound Analyzer. This Analyzer is based on fast Fourie transformation and virtual instrument technique.As an application, combining software and hardware, all kinds of weight noise sound level measurement and real-time noise octave analyzes realized synchronously. The design method has been introduced from three ways, which includes hardware, software and panel. An applied example and error analyze of Virtual Sound Intensity Analyzer are given.This Analyzer is low cost, small volume. and it is also easy to operate. It can be widely used in actual applications.