According to the basic principle of patent law, only one patent right can be granted for the same invention. When two or more people file separate patent applications for the same invention, there are two principles: the invention priority principle and the application priority principle. The principle of prior invention means that if two or more people file a patent application for the same invention, the patent right shall be granted to the person who made the invention first, regardless of the time when he filed the patent application. However, when adopting this principle, we often encounter many practical difficulties in determining who is the first inventor. Therefore, at present, only a few countries in the world, such as Canada and the Philippines, adopt this principle. The principle of first application means that when two or more people apply for the same invention respectively, the time of making the invention is not asked, but the time of filing the patent application shall prevail, that is, the patent right is granted to the first applicant, which is the practice adopted by most countries in China and the world.