Abstract: The quality of service (QoS) of Web services that serve the Internet business is inherently uncertain, which increases the difficulty of QoS-aware Web service composition optimization problem. Assuming that QoS and its aggregation of services are normally distributed, the calculation methods of expectation and standard deviation of the addition, maximum, minimum and multiplication of two independent normally distributed random variables are focused and a QoS-aware robust Web service composition optimization model is built. By overloading the addition and subtraction operators, and choosing suitable fitness function, a discrete particle swarm optimization algorithm with constraints is designed to solve the model. The simulation experiments illustrate that the model has a good accuracy and the composite service gained has a good robustness.