Abstract: Analog realization error and channel mismatch error comprised of offset error, gain error and time error are the two key kinds of error sources in frequency interleaved analog to digital converter (ADC) systems, resulting in the systems' global performance degeneration. In this paper, intensive study is carried out on the errors in frequency interleaved ADC systems. On the one hand, it shows that the virtual frequency response of the sampling filter leading to the realization error is mathematically calculable. On the other hand, it also reveals that the channel mismatch error will give birth to the regular appearance of the spurious noise peaks in the spectrum of the output signal. Both the theoretical derivation and simulation verification certify that the spurious noises caused by the gain error and the time error occur at the same frequency location but not that of phase, and the peak amplitude caused by the offset error has nothing to do with the input signal frequency. The research results will promote the development of error compensation and calibration.