Abstract: A kind of virtual oscilloscope which has flexible adding function, short update cycle, amazing performance was designed base on Visual basic 6.0 because of several disadvantages of traditional oscilloscope, such as limitations of function, expensive price, long update cycle and so on. This system includes data acquisition, display of spectrum of voltage waveform, display of voltage waveform, fast Fourier transform algorithm, data saving or reading and parameters processing revealing. A test of data collection and waveform display has been made between virtual oscilloscope and traditional oscilloscope. The results of detect signal are consistent. Besides friendly graphical user interface, easy operation, brilliant function adding, inexpensive cost and small wave distortion, the virtual oscilloscope can measure the spectrum of the signal and save or read tested data as well.