The restriction of mortgage of houses and real estate is based on the provisions of the Guarantee Law. Where a party mortgages the property specified in Article 42 of this Law, it shall register the mortgaged property, and the mortgage contract shall take effect from the date of registration, that is, the mortgage shall take effect from the date of registration. Therefore, the starting date of the real estate mortgage period is the effective date of the mortgage contract registration. In addition, according to the "Reply for Instructions on Other Ownership Certificates" issued by the Real Estate Department of the Ministry of Construction 1995, the mortgage period in the property ownership certificate should be the period for the debtor to perform the debts agreed in the mortgage contract. The date when the mortgage period of real estate expires is the time limit for the debtor to perform the debts agreed in the mortgage contract. Therefore, the real estate mortgage period takes effect from the registration date of the real estate mortgage contract to the expiration date of the debt performance period of the main contract. At the same time, according to Article 52 of China's Guarantee Law, the mortgage right coexists with its secured creditor's rights, and if the creditor's rights are eliminated, the mortgage right is also eliminated. Therefore, the term of real estate mortgage starts from the effective date of the registration of real estate mortgage contract to the date when the main contract debt is eliminated.