Reliability of a software system is an important attribute of software quality, and its importance has increased significantly due to the growing demand for high-quality software systems. Evaluating reliability during the design phase is essential for improving system performance and ensuring effective planning. At this stage, an important challenge is to identify suitable methods for achieving the desired reliability of the software system. Reliability allocation methods can be applied to assign reliability targets to individual components prior to the actual system design. To address this, a new hierarchical model is proposed that integrates the perspectives of users, software programmers, and software managers. The system is decomposed into multiple levels, including functions, programs, modules, and submodules, to enable systematic analysis. To handle uncertainty and vagueness in human judgments, the fuzzy analytic hierarchy process (FAHP) is employed, incorporating the geometric mean method with trapezoidal fuzzy numbers. The proposed approach determines reliable weights and effectively allocates reliability targets at each level. A comparison with the classical AHP method demonstrates that FAHP provides a more flexible and realistic representation by capturing uncertainty, making it more suitable for reliability allocation in complex software systems.