Non-Surgical root canal therapy is the priority for the management of pulpal disease. Calcified root canal therapy is one of the most challenging among root canal therapy. It usually leads to treatment failure because clinicians cannot precisely passing through the root canals and get detailed cleaning and shaping to eliminate the bacterial infection in the root canal systems. Here, we provided a non-surgical root canal treated case, maxillary first molar with calcified distobuccal canal, combined cone-beam computed tomography (CBCT) and dental operating microscope. Using calculate and analyze three fault sections between the top and bottom of the calcified canal from CBCT, we successfully found the distobuccal root canal pathway and successfully saved the tooth. We also analyzed published researches to provide information for clinicians facing calcified root canal therapy.