In order to share doctors' experience in diagnosis and treatment, the paper studies the construction of the auxiliary diagnosis system from the perspective of similar Electronic Medical Records(EMR), and introduces the system's functional modules and theoretic algorithms, including computational algorithms for the similarity of complaints, similarity of diagnosis and treatment modes, image similarity and comprehensive similarity. This method can compute the similarities comprehensively according to contents of EMR. The EMR retrieved can serve as reference for doctors to make a plan for diagnosis and treatment.