Reasonable allowance design of forgings can reduce the loss of scrap during the trial production of new products as well as reduce the consumption of metal materials and machining cost. Therefore, according to spatial vector summation algorithm, a new allowance design method of hot rolled ring forgings based on data statistics was proposed, which regarded the size deviation in geometry direction of hot rolled ring forgings and the surface defect of product as the spatial geometry vector, and the summation of these vectors produced the minimum machining allowance of hot rolled ring forgings. Then, these vector values were obtained by the measurement and statistics of the products produced by the production line, representing the actual production capacity of the production line, and according to the probability density of normal distribution, the final size qualification rate of product could be predicted. Furthermore, compared with the existing allowance design method, this allowance design method was based on the product data produced by the production line, and the designed rolled ring forgings allowance was more suitable for the accuracy requirements of the production line. The results show that the application of this method can avoid the excessive or insufficient allowance during the trial production of new product and effectively reduce the material waste or scrap waste, which can also be used in other products such as die forging and free forging.