The invention provides an inside liner online thickness measuring and width measuring device, which is characterized in that the inside liner online thickness measuring and width measuring device comprises a bracket, wherein a driving device and a fixed frame are arranged on the bracket; a roller is arranged in the middle of the fixed frame and is fixed by means of a roller bracket; a first thickness measuring sensor arranged above the roller and a second thickness measuring sensor arranged below the roller are arranged on the fixed frame; and the driving device drives the fixed frame to do reciprocating motion along a direction perpendicular to a conveying direction of an inside liner, so as to drive the first thickness measuring sensor and the second thickness measuring sensor to do reciprocating motion relative to the inside liner on the roller. The inside liner online thickness measuring and width measuring device and an inside liner online thickness measuring and width measuring method provided by the invention can realize comprehensive online detection of products, reduce the labor intensity of workers and improve the quality of the inside liner.