Is it legal to sell the property basement?

That depends on the function of the basement and whether there is an independent property right certificate.

If the basement belongs to residential, commercial, warehouse and other special purposes in planning, and the ownership is registered in the housing management department, then it is legal to sell the basement.

In fact, many basements of commercial buildings are for sale, especially large commercial buildings, shopping malls, shopping centers and so on. Basement belongs to ordinary commercial units, which are sold and rented like houses on the ground. They are all formal properties with real estate licenses.