A next generation B factory and the detector counterpart, SuperKEKB and Belle II, are being built in Japan, as the upgrades of KEKB and Belle, respectively. The new collider will start its commissioning in 2015. This is an ambitious project. The luminosity of the e(+) e(-) collider will be upgraded by a factor of 40, which will create a 50 times larger data set compared to the Belle sample. Both the background and the triggered event rates will be increased by a factor of at least 10. The Belle II software system is designed to accommodate these challenges and to run on grid, cloud, and local resources around the world. Various external software packages are employed to enhance the user interface. The software system, basf2, is structured as a framework built with dynamic module loading and the ability of parallel processing. The system is written in C++ with Python steering scripts, compatible with common Linux operating systems. A full detector simulation library is created based on Geant4. In this paper, we will explain the design of the Belle II software structure and the current status of the software development.