To study the data uncertainty in SFEP (system fault evolution process) and the causes of data uncertainty, the method of quantum mechanics was used to analyze it. Firstly, the composition and hierarchy of SFEP were described. Secondly, the timeliness and characteristics of SFEP were studied, as well as the causes of data uncertainty. finally, the formal logic of SFEP in quantum state and the causes of data uncertainty were studied. The results show that SFEP is hierarchical and can be expressed as quantum superposition states. Measurement makes SFEP lose its future state and generate historical state. The historical state is calibrated by time, and the future state is in the factor space and has nothing to do with time. Data uncertainty is caused by the delay time between measurement and application; Different formal logic leads to different superposition modes of quantum states, which leads to data uncertainty. Therefore, time and formal logic are the fundamental reasons for SFEP to produce uncertain data.