The invention relates to an inertial elbow thick-thin powder separator, which belongs to the technical field of power conveying and burning. The separator comprises a core barrel, an open guide elbow and ribs; the core barrel is a closed straight barrel, one end of the open guide elbow is connected with the core barrel, and the ribs are fixed on both sides of the open guide elbow, and are outspread. The cross section of the open guide elbow is shaped like a non-closed circular arc or polygon. The separator with a simple structure has a good thick-thin separation effect on two streams of powder, the distribution of the thick stream of powder is uniform, and the separator is applicable to gas-solid conveyers which are provided with elbow structures and need thick-thin separation, such as thick-thin pulverized coal cyclone burners and cement industries.