Abstract: With the increasing demand of nuclear power plant containment pressure resistance performance, the tonnage of nuclear power plant containment prestressing is also increasing. The number of single strands in third-generation nuclear power plants has reached 55. When the number of strands and the bending undulation gets large, stress relaxation occurs between the strands due to different lengths, which in turn produces uneven stresses. In this paper, equal stress tensioning method was proposed. Equal stress tensioning method requires the use of an equal stress jack, consisting of multiple small cylinders of equal tensioning piston area in parallel, using the principle of equal oil pressure in the parallel oil circuit to achieve the same pressure applied to each strand by each small cylinder. The implementation of the equal stress tensioning method is characterized by cyclic reciprocal equal stress tensioning of all strands until all strands reach the same preset stress, and the equal stress state is judged by the fact that the length of the strands does not change during tensioning. In order to understand the distribution of the stress of each individual strand after equal stress tensioning, a test method was designed to measure the pressure of a single piston in the equal stress jack, connected the piston rod of the equal stress jack to the extrusion head and the load cell, acted on the reaction frame, gradually increases the oil pressure of the equal stress jack pump, read the value of the load cell, and then measured the individual piston force of the equal stress jack. Then, by using a specific jack to tension test the steel bundle that has undergone equal stress tensioning, the single strand stress data were collected, the standard deviation of the single strand stress data were formed, and the data were analyzed to finally obtain the distribution of the single strand stress after equal stress tensioning when prestressing tensioning is performed. The analysis results show that the equal stress tensioning method proposed in this paper for large tonnage prestressing in nuclear containment can make the stress distribution of single strand steel strand during tensioning more uniform, the maximum stress relative deviation is within 5%, and the greater the tensile force of equal stress tensioning, the more uniform the stress distribution of steel strand during tensioning. In the prestressing project of third-generation nuclear power plants such as Hualong 1, the equal stress tensioning of steel strands before tensioning operation can effectively ensure the quality of prestressing tensioning of 55 holes with large tonnage, and thus ensure the safety of nuclear power plants in emergency situations.