Service composition is effective in constructing value-added service rapidly for service-oriented applications. Existing selection models for composite services rely severely on assumptions that customers each requirement is raised alone, while in reality, service requirements can be numerous in practical applications. And when a small time slide is focused on, multiple requirements can be seen as concurrent and service sets involved by sub-solutions corresponding to each individual requirement have intersections, resulting in competitions or sharing of certain services between requirements. Therefore, current single requirement-oriented methods can not deal with the situation that multiple service requirements arrive concurrently competing for services. This paper presents a multiple service requirements-oriented service composition model and algorithm. In the light that service can either be exclusive or sharable and decisive priority relations exist between all assessment factors, an assessment method based on confliction-avoidance scheduling and graded weighting priorities is put forward. On that basis, tradeoff strategies are proposed for genetic algorithm and a service composition method is put forward for tradeoff between satisfactions of multiple service requirements. Experiment results show that this method ensures proportionality of all sub-solutions and sub-optimal solutions can be gained efficiently by improving its coding manner. Compared with other possible strategies, it has proved superior applicability to different circumstances of quantity and quality of available services.