Paleostress field is one of the key aspects in the geodynamic analysis, and paleostress inversion of fault-slip data has been becoming an important approach in the reconstruction of paleostress field and improved greatly as well as employed widely in last two decades. There are, however, still many problems remain controversial, such as, strain or stress interpretation of the inversion results, impact factors controlling the inversion results and their errors. In this paper, the main factors affecting the result of paleostress inversion of fault-slip data are summarized as pure shear or simple shear strain regime, shear fracture type among Riedel shear system, length-to-width ratio of fracture and weak fabric or pre-existing fractures within geologic terrane as well. Comprehensive errors of paleostress inversion both from primary fractures and pre-existing weakness planes have been quantitatively analyzed in detail. It is proposed that the inversion results could be interpreted as stress states if the pure shear or simple shear regime can be clarified or the deviation is within the limit of error. Quantitative analysis in this paper implies that the inversion errors of principle stress direction should be confined less than 35° if the data were collected from faults formed under a specific tectonic stress filed. In other word, the inversion results with a direction deviation less than 35° could be grouped into one generation of paleostress field, if there is no evidence indicating that they were derived from different tectonic deformations.