This book deals with the investigated on a stellar model with Kramer’s opacity and negligible abundance of heavy elements. This book contains the mechanism of energy production in a star and energy transports in stellar interior. In addition these studies solve radiative layers and convective layers equation and comparing them. These studies have drawn a curve in the U-V plane with the core solution for determining the value of constants. Finally in this book this study determined the structure of a star of 2.5 solar masses in which this study chosen Keamer’s opacity and the abundance of heavy elements are negligible.