20 1800。 According to the postcode database of Jiading District, Shanghai, the postcode of Jiading, Shanghai is 20 1800. The first two postal codes represent provinces, autonomous regions and municipalities directly under the central government, 20 represent Shanghai, the third represents postal codes, the fourth represents city and county numbers, and the last two represent mail delivery offices and offices. More than 140 countries in the world have successively implemented the postal coding system, which can be used as one of the standards to measure the communication technology and postal service level of a country.