Trustworthy service flow is an important content of the trustworthy software theory, and it is also a key point to achieve service-oriented computing currently. For meeting the diverse trustworthy requirements of consumers, using fuzzy set to describe the trustworthiness attribute of service is proposed. According to the theory of fuzzy set, the trustworthiness of service flow is computed and evaluated, and the similar service and similar service flow are defined. Constrained by the quantitative assessed trustworthiness and normalized QoS attributes, trustworthy service flow problem is formalized as the NPC problem, which is proved in terms of NPC problem definition. Then, a novel algorithm Hybrid QPSO is put forward for solving the trustworthy service flow problem. To illustrate the feasibility, and effectiveness of our approach, we take the travel service flow as an example to test, and compare the execution result of HQPSO algorithm with the backtracking algorithm and greedy algorithm.