Based on the single wall carbon nanotubes (SWNTs) films prepared by chemical vapor deposition, a flexible strain sensor with sandwich structure was prepared using polydimethylsiloxane (PDMS) as substrate, which has outstanding optical transparency and resistance response. The effects of different SWNTs layers on sensor performance were investigated. The experiments show that with the increase of the SWNTs film layers, light transmittance and resistance response of the strain sensor gradually reduces. The strain sensor obtained from a single layer of SWNTs film has the largest change of resistance, which amount to 100% at strain of 10%, even at small strain (2%) still detect a significant change in resistance (18%). The strain sensor has excellent outstanding durability and is used to detect the motion state of human body, it has potential applications in the areas of flexible electronic skin.