Planetary roller screw mechanisms are precision transmission components that facilitate the conversion of rotational motion into linear motion and vice versa. Due to their high precision, load-bearing capacity, and extended service life, PRSMs are extensively used in advanced applications such as aerospace, weapon systems, ships, humanoid robots, and machine tools. Currently, the primary contact method between the threads of PRSMs is point contact, which subjects a limited number of roller teeth to elevated contact stresses during operation. In contrast, line-contact PRSMs offer a larger contact area between the threads, enabling significantly lower contact stresses compared to point contact, thereby enhancing load-bearing performance. However, the thread contact in line-contact PRSMs is linear, similar to conical roller bearings, which leads to edge stress peaks. These peaks considerably reduce the load-bearing capacity of PRSMs and may ultimately result in failure of the thread surfaces. Therefore, it is essential to propose an effective thread profile modification method to reduce edge contact stresses and mitigate the stress peak phenomenon in line-contact PRSMs. Previous studies have shown that utilizing an improved logarithmic modification curve can effectively lower contact stresses at the edges of thread teeth in line-contact PRSMs. Moreover, due to the multi-component engagement characteristics inherent in line-contact PRSMs, the outcomes of various modification combinations can vary significantly. A modification combination that applies the logarithmic curve only to the rollers, while leaving the screw and nut unmodified (RLM), has demonstrated substantial reductions in contact stress. This indicates that using effective modification curves based on the RLM can alleviate edge stress peak phenomena in line-contact PRSMs. To further reduce edge contact stresses in line-contact PRSMs, this study proposes several improved modification curves based on the geometric characteristics of the line-contact thread teeth. Finite element simulations are employed to analyze the performance of various modified PRSMs under the RLM modification combination. By comparing the results of different modification curves, the study aims to identify the optimal modification curve. Additionally, a control variable analysis of the parameters constituting the optimal curve is conducted to determine the best modification strategy. This research aims to provide important design insights and theoretical support for the mechanical design of high-performance planetary roller screws with low contact stresses.