To accurately calculate the contact stress of the five-ball fatigue testing machine tooling,the tooling design contact angle is determined by the geometric size relationship. According to the load deformation relationship and the formula derived,the balance equation is established between the external load and the working contact angle. The equation is solved using the iteration method. The working contact angle under load is calculated,and the tooling contact stress is obtained. For the actual size of the 9. 525 mm diameter steel ball tooling,the contact stress comparative analysis is calculated by the numerical algorithm and finite element method respectively. The calculation result deviation is less than 2%. It shows the contact stress numerical algorithm is reliable,it can be used for the test protocol formulation and provide guidance for the test tooling design.