The contract number can be inquired through online inquiry, intermediary assistance inquiry, on-site inquiry, online signing platform inquiry, etc.

1. Online inquiry: Log in to the official website of the local housing authority or real estate trading center. Many areas provide online contract inquiry services. Enter the necessary information, such as the name of the property owner, ID number, property certificate number, house address, contract signing time, etc. After verification, the online contract number can be queried.

2. Intermediary assistance in inquiry: If you buy or sell a house through a real estate agency, you can contact the intermediary company and ask them to assist in inquiry of the online contract number. You may need to provide relevant transaction information.

3. On-site inquiry: Go directly to the local housing authority office hall for inquiry. Remember to bring your ID card, real estate certificate and other relevant documents and the original contract.

4. Online visa platform query: Enter the online visa number and password obtained during the online visa application, and log in to the Housing and Urban-Rural Development Bureau or other designated online visa platform website to query.