Personal data tort cases are restricted by algorithm black box and technical barriers, and there are some serious defects in the fact-finding of causality, such as the failure of standard of proof and abuse of free evidence. Bayes' theorem uses mathematical principles to accurately calculate causality, more accurately analyzes evidence with accurate prior probability and likelihood ratio, converts evidence and facts into probabilistic statements to enrich the material for judges to form free mental evidence, and conforms to the proof principle of causality in personal data tort cases. Taking Bayes theorem as an important tool of evidence reasoning and fact-finding, it is helpful to build a new methodology for determining causality in personal data tort cases. These are practical and feasible paths to integrating Bayes' theorem into Chinese judicial practice: reconstructing the epistemology and methodology of fact reasoning to break through the cognitive barrier, adopting the case guidance system as the normative path, and integrating Bayes' theorem into intelligent justice to expand the fact-finding method.