Biomass is a renewable energy source which, arising from a range of organic products such as forest residues, wastes or purpose grown crops that can be converted to heat, power or other fuels, provides a substitute for fossil fuels so as to mitigate the global environmental pressure. Many countries have gained significant achievements and valuable experiences in biomass energy research and application. Greater attention is paid on the overall effect and influence on our energy structure, society, economy and environment. In the paper an outline of the biomass energy system research and development in some developed countries in recent years is presented, and especially puts emphasis on the system engineering methods and technologies which are imperative to implementing sustainable development strategies for humankind to make a sustainable world.