© 2019, Springer Nature Switzerland AG. In this study, we sought to develop a system to evaluate the workload of multiple sequential tasks using a digital human and muscle fatigue model, as well as test its validity using a sequential task experiment. The muscle fatigue model is the three-component model introduced by Xia et al. The model assumes that the muscle motor unit consists of resting, activated, and fatigued components. We used a temporal smoothed value of the active component ratio to the non-fatigued component to estimate workload. A system was developed using this model to evaluate workload of any combination of sequential tasks of the single manual handling task. A sequential task consisting of three kinds of material handling task performed by a digital human and real environment was prepared as a validity test. We found that the estimated workload using the simulation and the subjective scores showed a similar pattern with the load of the sequential tasks and repetitions.