An expert system is a computer software that has a knowledge base. Where knowledge is taken from several experts with experience working for years on a particular field of expertise. Expert systems easier to develop and specifications are not too difficult, so it can be used by computers that exist todayThe purpose of this study to design a software tool in diagnosing damage to the machine canon NP 6650XX which creates the appearance of an error code on the monitor screen machine using Dempster Shafer Method. To achieve this, research is conducted by collecting the theories associated with this machine, based on the theory of knowledge, undertake steps that expert system development, identification, conceptualization, formalization, implementation and testingThe result is a software that can provide information about damage to the machine canon NP 6650XX which such damage can lead to the appearance of an error code on the monitor screen machine.  Keywords: Expert System, Knowledge, Canon Machinery, Error, Dempster Shafer.