The invention relates to the field of biosensing technology, concretely relates to a biological sensing system based on 45-degree dual drive symmetrical structure photoelastic modulation, and the system realizes original position, rapid, high precision, high sensitivity, high repeatability, low cost, and control convenience during measurement process. The system comprises the following components:detection laser, a polarizer, a biochemical reaction tank, a microflow syringe pump, an adjustable slit, a photoelastic modulator, a polarization analyzer, a photoelectric detector, an FPGA control module, and a control computer; the biochemical reaction tank is packaged by semicylindrical mirrors and silicon wafers at interval with PDMS; a flowing channel and an outputting channel are also constructed, two channels are connected to the microflow syringe pump, the photoelastic modulator is a photoelastic modulator with a 45-degree dual drive symmetrical structure, the structure comprises a dual drive piezo electric crystal and a photoelastic crystal which form a 45 degree angle, and the piezo electric crystal is connected to an FPGA control module by an LC resonance high voltage control circuit. The product is mainly applied to the aspect of biosensing.