In this study, the ultimate strength, initial stiffness, and failure mechanisms of tubular T/Y-joints reinforced with doubler plate under axially compressive load are numerically investigated. At the first step, a finite element (FE) model was developed and verified against the data available from eight experimental tests. At the next step, 210 FE models were generated and analyzed to evaluate the effect of joint geometry and doubler plate size on the static strength of doubler plate reinforced T/Y-joints under axially compressive load. Results showed that the ultimate strength of a doubler plate reinforced T/Y-joint can be up to 295% of the strength of the corresponding unreinforced joint. Also, doubler plate reinforcement method can considerably increase initial stiffness and improve the failure modes of tubular T/Y-joints subjected to axially compressive load. Afterwards, the deformed shapes of doubler plate and collar plate reinforced T- and Y-joints are compared. Despite the considerable effect of the doubler plate on the static strength, its feasible application during the joint fabrication, and the frequent usage of CHS T/Y joints in offshore jacket-type platforms, the ultimate strength, initial stiffness, and failure modes in doubler plate reinforced Y-joints under axially compressive load have not been studied. Also, so far no design equation is available to determine the ultimate strength of T- and Y-joints reinforced with doubler plate under the axially compressive load. Hence, after the parametric investigation, a new formula is derived, through nonlinear regression analysis, to determine the ultimate strength in such case.