For studying operational and organizational systems, modeling and simulation tools are becoming increasingly relevant. It is possible to build a lot of systems and study their behavior, which saves a lot of effort, time, and cost, where it cannot or difficult to study its behavior in the real world. There are many frameworks to implement modeling and simulation using a computer. in this paper DEVS-Suite for discrete events is used to implement a simulation of cargo unloading problem which represents a study on estimating the optimal number of trucks and cranes required in process of unloading goods and according to some determinants. The duration of the simulation is one month which is equivalent to 43,200 minutes. Based on the performance measures that were adopted in this study, the optimal number of trucks and cranes is 5 out of three assumptions of 3, 5, and 10, where the work will be in a permanent state of work and high productivity.