Whether the contract concluded between the administrative organ and the people belongs to the administrative contract or the private law contract in public law, there is often a dispute in practice. This paper believes that in order to alleviate the problem of qualitative disputes, it should be possible to introduce the freedom of choice of the legal form of the administrative organ and the freedom of choice in the trial procedure. Respect the legal form of the contract between the administrative organ and the people to maintain the transparency and stability of the legal order and quickly resolve the contract dispute. The types of administrative contracts recognized in the current practice include employment contracts for contracted personnel, administrative contracts for public schools and teachers, public expense contracts, commissions for the exercise of public power contracts, special hospital contracts for universal health insurance, commissioned industrial zone contracts, and incentive investments. Investment contract for the construction of the market, agreement price purchase contract before land acquisition, settlement contract on tax law, guarantee contract for administrative execution procedures, animal sterilization contract, etc. The legal effect of the current administrative contract concerning illegality should not be dealt with rigidly. Instead, the principle of proportionality in administrative law should be upheld. First, the “contract adjustment” should be tried. In order to considerate balance to be adjusted by the parties t, it will be invalid.