The invention relates to the field of measurement instruments, in particular to a radius measurement device of an annular block. The radius measurement device comprises a machine body and a transmission cavity, wherein the transmission cavity is formed in a top wall of the machine body, four groups of sliding grooves are annularly formed around the transmission cavity, inner diameter measurement devices are arranged in the sliding grooves and are used for fixing the annular block, the inner diameter measurement devices are used for locking the annular block and simultaneously driving a first counter arranged in a bottom wall of the machine body to count, and the inner diameter of the annular block is obtained after a numerical value of the first counter is processed. With the radius measurement device of the annular block, provided by the invention, automatic fixing and centering of the annular block can be achieved by the power source, the inner diameter measurement of the annular block is achieved, the external diameter measurement of the equipment is driven by continuous rotation of the same power source, a round ring can be accurately centered by the equipment, so that the equipment is higher in measurement accuracy; and meanwhile, the equipment employs an automatic measurement mode and is more stable, and production, promotion and application are facilitated.