Powder-forged connecting rod with a complex geometry shape always has a problem with nonuniform density distribution. Moreover, the physical property of preform plays a critical role for optimizing the connecting rod quality. The flow behavior of a Fe-3Cu-0.5C (wt pct) alloy with a relative density of 0.8 manufactured by powder metallurgy (P/M, Fe-Cu-C) was studied using isothermal compression tests. The material constitutive equation, power dissipation (η) maps, and hot processing maps of the P/M Fe-Cu-C alloy were established. Then, the hot forging process of the connecting rod preforms was simulated using the material constitutive model based on finite element method simulation. The calculated results agree well with the experimental ones. The results show that the flow stress increases with decreasing temperature and increasing strain rate. The activation energy of the P/M Fe-Cu-C alloy with a relative density of 0.8 is 188.42 kJ/mol. The optimum temperature at the strain of 0.4 for good hot workability of sintered Fe-Cu-C alloy ranges from 1333 K to 1380 K (1060 °C to 1107 °C). The relative density of the hot-forged connecting rod at the central part changed significantly compared with that at the big end and that at the small end. These present theoretical and experimental investigations can provide a methodology for accurately predicting the densification behavior of the P/M connecting rod preform during hot forging, and they help to optimize the processing parameters.