The theory of injecting dither signal was analyzed to improve the performance of ADC. An appropriate dither signal was selected to inject into the ideal quantized model. The simulation demonstrated that the dither injecting technique could randomize the periodic triangular distribution of quantization error. In the practical application of the dither injecting technique, firstly, the dither injecting simulation was completed based on 10 bit 25 MS/s pipelined ADC model, and the SFDR of ADC was improved from 7469 dB to 85 dB. Then, the dither injecting test was carried out for two kinds of ADC chips. The SFDR of ADC chips were increased by 829 dB and 597 dB respectively depending on dither injecting technique. The experiment gave a conclusion that the dither injection technique could significantly improve SFDR of ADC, made a full preparation for the integration of noise circuit module into ADC.