In addition to Article 20 of the Patent Law of People's Republic of China (PRC), the date when the patent administrative department in the State Council receives the patent application documents is the filing date, Article 28 also stipulates that "if the application documents are mailed, the postmark date sent shall be the filing date." In other words, the application date is the date when the applicant submits the application documents to the post office.
In practical work, the postmark is often vague, unable or difficult to identify. In this case, if the applicant can provide evidence of the exact date of submitting the application documents to the post office, the time when the patent administration department in the State Council receives the applicant's mail is generally the filing date. Article 4 of the Detailed Rules for the Implementation of the Patent Law of People's Republic of China (PRC) stipulates: "All documents mailed to the patent administration department in the State Council shall be submitted on the date of mailing. If the postmark date is unclear, the date of receipt by the the State Council Patent Administration Department shall be the filing date, unless the parties can prove it.