Abstract: The method of presumption of intention is adopted by the World Anti-Doping Code to identify non-specific substance anti-doping rule violations. In order to reduce or even eliminate the standard sanction, the athlete should burden the proof of disproving intent. However, the uncertainty of conditions needed for non-intentional proof leads to a strict identification of athletes' burden of proof, making the non-intentional proof a "highly impossible task". According to this, some practical decisions have taken steps to modify the strictness of rules concerning non-intentional proof, by weakening the precondition of establishing the source of prohibited substance, or varying the acceptable methods of proof used by athletes. The 2021 World Anti-Doping Code responds to this new trend, but the uncertainty for athletes remains. To solve the dilemma of proof, it is suggested that subjective factors should be taken into consideration properly in the following aspects: expanding the rule of non-intentional anti-doping rule violations, strengthening the principle of free proof and considering the standard of "cost and benefit" to reach a more realistic approach on the balance of probabilities. All above are helpful to improve the rationality of dealing with anti-doping rule violations and promote the formation of a more fair and just anti-doping rule system.