Abstract: The principle of contract relativity is regarded as the standard, and it is the basic adherence of the two major legal systems in modern times. However, strict adherence to the principle of contractual relativity not only hinders the convenience of transactions, but also increases the complaints of dispute resolution. The origin of pure reason and the call of practical reason require the social reality, from the strict adherence of contract relativity to the recognition of exceptions, the trend of legislative reform in various countries is generally consistent. The adversarial principle of contract does not completely negate and exclude the relative nature of the contract, but as an external supplement, which is of great significance to perfecting the contract fulfillment system, adapting to the involuntary theoretical thoughts of creditor's rights, and meeting the ever-changing trading needs. The three-person contract and the subrogation of the creditor are the internal breakthroughs of the principle of contract relativity. They break the limitation that the traditional contract theory only has effect on the parties, make up for the shortcomings of strictly adhering to the principle of contractual relativity, and achieve a balance between protecting the transaction security and protection of creditors directly. The external supplement is called “outside”, but in fact it is the filling of the internal system of the contract law, because it is the perfection of the basic principles of the contract law; the internal mitigation is called “inside”, but in reality it is the construction of the external system of the contract law because the formation of a complete contract fulfillment system is of great significance. One inside and one outside together build the bone and soul of the exception of the principle of contract relativity.