Abstract: High harmonic generations (HHG) in atoms, molecules and nanostructures open a new field in nonlinear optics. Its ultrafast response time and high energy scale attract enormous attentions. At this time, the field is still growing and many potential problems are not yet solved. This paper first briefly introduces this new topic, then presents a simple example to explain the famous radiation cutoff equation, and finally uses C60 to show the details how to compute the radiation from the simulation.