Optical fiber communication technology has occupied the main position of the current communication transmission. But the single mode optical fiber (SMF) communication system based on wavelength-division-multiplexing (WDM) technology is now facing severe channel capacity crisis. Therefore, mode-division-multiplexing (MDM) technology based on the multimode or few mode fiber (FMF) has got the attention of many researchers. Mode Converter (MC) is one of the most important components in MDM technology, and long period fiber grating (LPFG) is a perfect all-fiber mode converter. The LPFG is used to convert LP01 mode to LP11 mode, and the multimode fiber is also used to eliminate inter-mode interference phonemenon in this mode converter. By using this mode converter, the converted mode has higher purity and better stability. The mode conversion efficiency reached 99.5% and there is no inter-mode interference phenomenon between these two modes. This MC device has good sensing characteristics, and this device has good linear sensitivity of strain, it can reach to 2.83 nm/N and 5.66 dB/N. So it can be concluded that this novel structure has excellent performance and will play an important role in the future application of optical fiber MDM and sensing field.