The invention relates to an optical fiber fluorescent biological sensor, which is composed of an excitation light path, a detection light path and a fluorescence receiving light path, and the three light paths are respectively connected to three branches of a Y-shaped optical fiber. On the excitation optical path, the excitation light source is coupled to one branch of the Y-shaped optical fiber by coupling optics; on the detection optical path, the other branch of the Y-shaped optical fiber is connected to the carrier or sample pool for immobilizing the biological recognition agent and performing sample detection; On the fluorescence receiving optical path, the third branch of the Y-shaped optical fiber is connected to the data acquisition system, and further connected to the signal processing and display system. The sensor has fast response, high sensitivity, good selectivity, light weight, small size, and is biologically friendly. It is suitable for all current fluorescent markers and can overcome the outstanding defects of traditional fluorescent markers such as short luminescence lifetime and photobleaching. It is widely used in Biomolecular recognition, medical clinical diagnosis, high-throughput drug screening, environmental monitoring, biochemical warfare agent detection and many other fields.