The invention discloses a room-and-pillar major-diameter longhole inverted-step-like segmented lateral caving subsequent filling mining method for a steeply-inclined medium-thick orebody and gently-inclined and inclined extremely-thick orebodies with steady surrounding rocks at upper and lower panels. The method is characterized in that: an orebody is divided into panels, then the panels are divided into continuous single-stage stoping units, and mining is carried out by using a stoping sequence of stoping one unit every other unit, i.e., mining a room at first and a pillar next; when mining a room, a V-shaped trench bottom structure is employed, a longhole drilling chamber is arranged at the upper part of stope, bar-shaped pillars are left to support the top plate of the chamber, a down-the-hole drill is used for drilling rocks, an explosion mode of light section VCR method underholing inverted-step-like lateral caving with a common emulsion explosive is employed, access roads towards the room for ore removal are arranged in the pillars, and cemented roof-contact filling is employed; and during stoping of the pillars, access roads for ore removal are dug towards the pillars in cemented bodies in the room, a stoping manner for the pillars is identical to that for the room, and non-cemented filling with tailings and waste is employed. The method provided by the invention has the advantages of high security, a low production cutting ratio, great production capacity, low operation cost and small loss and dilution of resources.