The invention relates to a blood collecting pen which stores blood collecting needles and can exchange the needles at the side. The blood collecting pen comprises a pen body, blood collecting needles arranged in the pen body, a trigger mechanism and a needle returning mechanism. The blood collecting pen is characterized in that the pen body is internally provided with a blood collecting needle bin which is internally and closely provided with a plurality of blood collecting needles by an elastomer; the pen body is provided with a needle disassembling device. Before use, the blood collecting bin is arranged in a blood collecting pen; when in use, a striking needle strikes the blood collecting needle at the armed position; after the stabbing work is completed, by opening a needle disassembling drawer at the side, the blood collecting needle separates from the blood collecting pen. When being used next time, the blood collecting pen can be directly used without installing the blood collecting needles. The blood collecting needle bin can be stored with seven blood collecting needles. After the seven blood collecting needles are used, next blood collecting needle bin can be exchanged. The blood collecting pen has a structure with a blood collecting needle storing bin and the needle disassembling device, provides convenience for disassembling the blood collecting needle, is more convenient when the consumed material is replaced for installation, and avoids the complex operation that when the traditional blood collecting pen is exchanged, the pen head of the front end needs to beunscrewed, then the needle is exchanged and then the pen head is installed.