Compared with traditional strain sensors, the flexibility, wearability, and real-time monitoring of flexible sensors are unique advantages. In recent years, flexible sensors have developed rapidly and are applied to medical detection, wearable devices, and many other aspects. Due to the excellent physical and chemical properties of polydimethylsiloxane (PDMS), it is often used as flexible sensor substrate. This article summarized the recent research work on the use of polydimethylsiloxane as flexible sensor substrate. Firstly, the sensing mechanism of PDMS nanocomposites was introduced in detail, including piezoresistive, capacitive and piezoelectric sensing mechanisms. Then the PDMS- based flexible sensors with carbon nanotube (CNT), graphene or nano- silver as nano- particles were reviewed. Finally, the research status and existing problems of PDMS- based flexible sensors were summarized and prospected.