In Recent years, global supply chain management has been a popular study area due to the economic globalization. This study mainly focus on the demand planning process of demand management in global supply chain management. The purpose of this thesis is to find the key factors and obstacles in demand planning process both in theory and practice, and solutions for the obstacles. Based on many scholar researches, a brief introduction of demand management and demand planning has been made at the beginning of the theoretical framework. Key factors, key obstacles and solutions are collected and clarified from empirical study and scholar researches in the theoretical framework. Qualitative approach is adopted as basic approach. We use case study to do the research and interviews to collect data. A server manufacturer of IBM named ISTC (International System Technology Corporation) is chosen as a case for this research. The key factors, obstacles and improvements of empirical study are compared with the facts of ISTC. New factors, obstacles and their new descriptions are figured out through the comparison between theory and the fact of the case. A suggestion for improvement and solution for the demand planning process is also put forward based on the empirical study and the facts of ISTC by this method.