Abstract: A ΔE(gas) E(solid) telescope with longitudinal double room ionization chamber is made. By double room technology, a higher energy resolution is achieved. Energy resolutions of 3.3 % for the ΔE detector and 1.5 % for E r detector are obtained by the in beam test with the elastic scattered 12 C from 197 Au at the energy of 50.3 MeV. Using it in ERD (elastic recoil detection )analysis, we analyzed some samples such as semi conductor GaAs,new photoelectric material GaN et al., and get depth spectra. This device can also be used as a monitor in ERD analysis with Q3D magnetic spectrometer to achieve higher resolution about 1 nm.