Abstract: A flexible strain sensor includes a substrate layer made of a flexible substrate and a conductive layer coated on the substrate layer. The conductive layer is made of ductile conductive metal material. An electrode is electrically connected to each of two sides of the conductive layer. A measuring device includes the flexible strain sensor, a measuring unit electrically connected to the electrodes of the flexible strain sensor by a signal line, and a processing unit coupled to the measuring unit. A method for producing a flexible strain sensor includes preparing a flexible substrate having a substrate layer. A conductive layer is formed on the flexible substrate by sputtering using silver, wolfram, or aluminum as a target material. An electrode of conductive material is formed on each of the two sides of the conductive layer. The electrodes are electrically connected to the two sides of the conductive layer respectively.