I wonder if it is legal for Gao Chun to rent out my farmland on the construction of expressway. How to calculate the lease term after the farmland becomes expressway?

According to China's land management law, you can use other people's land.

Article 2 The state may, according to the needs of public interests, expropriate or requisition land according to law and make compensation.

The state practices the system of paid use of state-owned land according to law. However, unless the state allocates the right to use state-owned land within the scope prescribed by law.

Fifty-seventh construction projects and geological exploration need temporary use of state-owned land or land collectively owned by farmers, which shall be approved by the land administrative departments of the people's governments at or above the county level. Among them, the temporary use of land in a planned urban area shall be approved by the relevant urban planning administrative department before approval. Land users shall, according to the land ownership, sign temporary land use contracts with relevant land administrative departments or rural collective economic organizations and villagers' committees, and pay compensation fees for temporary land use in accordance with the contract.

Users of temporary land shall use the land according to the purposes agreed in the temporary land use contract, and shall not build permanent buildings.

The term of temporary use of land is generally not more than two years.