Theory of acoustic phonon inelastic light scattering medium was used to study the cross sensitivity of temperature and strain in engineering application of distributed optic fiber sensor based on BOTDR. The theoretical relation model for Brillouin frequency shift with temperature and stress fiber was established. Numerical simulation showed that when the core refractive index increased, the Poisson's ratio decreased or the built in modulation layer increased, and the Brillouin frequency shift temperature and strain sensitivity decreased; when the core refractive index and the core Poisson′s ratio both decreased or the thermal expansion coefficient of built in modulation layer increased, the Brillouin frequency shift temperature and strain sensitivity increased. Based on this, experimental test system for Brillouin scattering measurement was constructed, and the built in modulation layer distributed fiber was tested with temperature sensitization and strain desensitization. Experiment result showed good consistency with simulation analysis.