擅自转租对出租人的所有权构成侵害，但承租人收取的租金不构成不当得利。

Unapproved sublet makes up infringement of title of lessor, but the rents collected by lessee don, t make up illegal profit.

youdao

第二十七条承租人在租赁期限内，征得出租人同意，可以将承租房屋的部分或全部转租给他人。

Article 27: the lessee may sublease all or part of the leased premises to others during a lease term, subject to the consent of the lessor.

youdao

第三十条房屋承租人可以将所租入的房屋转租他人，但须征得房产主同意。

Article 30 the lessee of a building may sublease the building he has rented to another person, provided that the consent of the owner of the building property must be obtained.

youdao