1, before paying the down payment, the buyer can ask the loan officer of the developer to input the online signing information into the computer to sign the contract. Before the input, if the house has been mortgaged by the project under construction, it is impossible to record the personal purchase information, that is to say, the developer has already rebuilt the mortgage. You can ask the developer to release the house first, and then pay the down payment to sign the online contract. 2. The land mortgage does not affect the online signing contract and the filing of the house purchase contract, but if the developer fails to pay off the land mortgage loan in the later period, it is impossible to apply for the real estate license. 3. Land mortgage refers to the legal act that the debtor guarantees the performance of the debt with the right to use the land. Land mortgage is the most basic form of real estate mortgage, which is generally carried out through land contracts. The essence of mortgage is a kind of security interest subordinate to the creditor's right, that is, a kind of security interest that guarantees the creditor to repay the debt with the property of others. 4. The mortgage of construction in progress refers to the act that the mortgagor obtains the land use right and the investment assets of construction in progress in a legal way as the guarantee for repayment of loans. Legal basis: Article 394 of the Civil Law of People's Republic of China (PRC) guarantees the performance of debts. If the debtor or a third party mortgages the property to the creditor without transferring the possession of the property, the debtor fails to perform the due debt or the creditor has the right to receive priority compensation for the property. The debtor or the third party specified in the preceding paragraph is the mortgagor, the creditor is the mortgagee, and the property that provides guarantee is the mortgaged property. Article 395 The following properties that the debtor or a third party has the right to dispose of may be mortgaged: (1) Buildings and other land attachments; (2) The right to use construction land; (3) the right to use the sea area; (4) Production equipment, raw materials, semi-finished products and products; (5) Buildings, ships and aircraft under construction; (6) means of transportation; (seven) other property not prohibited by laws and administrative regulations. The mortgagor may mortgage the property listed in the preceding paragraph together. Article 400 To establish a mortgage, the parties shall conclude a mortgage contract in writing. A mortgage contract generally includes the following clauses: (1) the type and amount of secured creditor's rights; (2) The time limit for the debtor to perform the debt; (3) The name and quantity of the mortgaged property; (4) the scope of the guarantee. Article 419 During the limitation of action for principal creditor's rights, the mortgagee shall exercise the right of mortgage. If it does not exercise, the people's court will not protect it.