The possible cases of invalid third-party governance contracts are covered by Article 52 of the Contract Law. In practice, "violation of mandatory provisions of laws and administrative regulations"is the most common situation. In the case of the above-mentioned contract invalidation, the results of judicial judgments are different, such as one of the pollutant discharge enterprises and the pollution control enterprises alone, the two parties, and the two parties jointly bear the environmental tort liability. Definition of environmental tort liability in the case of invalid third-party governance contract should firstly identify the "polluter" between the pollutant discharge enterprises and the pollution control enterprises according to the "literal range" of "pollution source control and discharge", and then determine its "polluter" liability according to law. For pollutant discharge enterprises or pollution control enterprises which do not conform to the "polluter" status, if there is evidence to prove that there is a common cause and effect relationship between them, they should bear the liability according to their share; if there is evidence to prove that there is joint infringement, joint danger, cumulative causality, or abetting or helping infringement with the "polluter", they shall bear joint and several liability; if there is evidence to prove that they are the "third party" with fault, they shall bear incomplete joint and several liability with the "polluter". The determination of the ultimate liability share between pollutant discharge enterprises and pollution control enterprises should be based on the degree of fault and the magnitude of the causal force, to solve the disputes in the definition of environmental tort liability in the case of invalid third-party governance contracts.