Using single radial immunodiffusion method to measure the Hemagglutinin Antigen (HA) content of influenza vaccines, the key is to determine the proliferation ring diameters. The traditional methods for the measurement of proliferation ring diameters use a vernier caliper or high-definition scans, which all have human disturbance that result in low measurement accuracy and stability. Based on machine vision technology, automatic measuring instrument for HA content is studied. The getting proliferation ring image by CCD camera and caculating the proliferation ring diameters by image processing, realize the operations automation and intelligence for acquisition of proliferation ring diameters data, calculation of HA content and analysis of results, which effectively improves the measurement accuracy, and eliminates the human disturbance. Experiments show that the measurement accuracy of this instrument is up to 2μg/mL, with relationship coefficient more than 0.99(R2>0.99), and high stabilization of less 1% coefficient of variation, that meets the measurement needs. The instrument is suitable for every kinds of HA content. The results are easy to store, transport, and easy to secondary treatment.