The invention discloses a cased well tractor crawling device used for crawling in a casing pipe. The cased well tractor crawling device comprises a gear sleeve assembly, a driving arm assembly and a brace rod assembly. The gear sleeve assembly comprises a driving bevel gear, a first driven bevel gear engaged with one side of the driving bevel gear, and a second driven bevel gear engaged with the other side of the driving bevel gear. The driving arm assembly is connected with the gear sleeve assembly and comprises a first transmission mechanism, a second transmission mechanism, a first crawling unit and a second crawling unit, the first driven bevel gear and the first crawling unit are connected through the first transmission mechanism, the second driven bevel gear and the second crawling unit are connected through the second transmission mechanism, the first crawling unit and the second crawling unit are oppositely arranged, and the first crawling unit and the second crawling unit have the same rotating speed but the opposite rotating directions and are used for grabbing or loosening the inner wall of the casing pipe. The brace rod assembly is connected with the driving arm assembly and slides in the axial direction of the casing pipe so as to drive the first crawling unit and the second crawling unit to be relatively staggered or get close.