The Doppler-free saturation fluorescence spectra system is set up. 100 kHz narrow-band dye laser and photodiode are used in this system. Two counterpropagating dye laser beams overlap on a Na cell whose temperature is set at 65 ℃. And a photodiode located at one side of the Na cell collects and detects the excited fluorescence. Then photodiode signal is sampled by data acquisition card which is controlled by LabVIEW software. Doppler-free features D2a,crossover and D2b are observed by scanning the dye laser frequency. When the dye laser frequency scan step is about 2 MHz,three lines in the D2a can be observed in this experiment.