Design method of the offline data analysis software based on LabWindows/CVI is introduced. The software realizes The software realizes the data reading and pretreatment, the display and adjustment of the waveform, the parameter measurement of the signal, and the analysis of the spectrum, power spectrum and harmonic distortion. Multithread technique was used to multiple tasks simultaneously of software. According to the results of the experiment show that the software has a friendly interface, the analysis results are correct and the performance is reliable.