Photonic time-stretch analog-to-digital converter (PTS-ADC) system utilizes the dispersion effect of fibers to stretch the sampled analog signal in time and compress its bandwidth, which can highly improve the sampling rate and bandwidth of electrical analog-to-digital converter (ADC). The PTS-ADC system needs a large length of dispersion fiber as the transmission medium, whose loss limits the signal-to-noise ratio (SNR) and effective number of bit (ENOB). Although it is possible to improve the system′s SNR by increasing the optical pulse power, the system can be influenced by the nonlinearity effect in fiber. The impact of the nonlinearity effect on the performance of PTS-ADC system including power transfer function and carrier-to-interference ratio (CIR) is analyzed from the theoretical, numerical and experimental results. It shows that the nonlinearity effect occurring in the first spool of dispersion fiber cannot distort the sampled analog signal, contrarily it can improve the system′s bandwidth and CIR. However, the nonlinearity effect in the second spool of dispersion fiber call deteriorate the system performance and should be refrained.