Biomass is a renewable energy source which can be an alternative energy to replacement fossil fuels. Biomass is combustible fuel but low density. Coal has a high Heating Value but has a weakness of difficulty to burn at low temperatures. One of the convertion of biomass and charcoal is the co-gasification method using mixture of biomass coconut shell and subbituminnus coal fuels with variation parameters of the composition. The reactor used is a fluidized bed bubbling reactor with a specification reactor diameter 160mm, Height 1230mm. The fuel variations used are (1) 66.7%:33.3% (2) 50%:50% (3) 33.3%:66.7%. The bed particles used are silica sand with an average diameter of 0.385mm. The results of the research by the boiling method of water show that the variation of fuel composition affects several parameters affecting the performance of a gasification reactor such as: In the fuel mixture 66.7%:33.3% effective flame can last for 40 minutes with an efficiency of 22.918%. For a fuel mixture 50%:50% effective flame can last for 58 minutes with an efficiency of 13.331%. While the fuel mixture 33.3%:66.7% of effective flame can last for 60 minutes with an efficiency of 9.433%
