We demonstrate a long-period grating(LPG) written on an index-guiding photonic crystal fiber(PCF) by CO2 laser pulse,which can produce multiple resonant peaks.The experimental observation and theoretical analysis both prove that these resonant peaks come from the coupling between the core fundamental mode LP01 and the core high-order LP11 mode.And we discuss the characteristics of two of the resonant peaks with different temperatures,curvatures,indices and tensile strains.A simple two parameter sensor,which is insensitive to the curvature and the index and can simultaneously measure the temperature and strain,is realized.The sensitivities to the temperature and the strain are 10 pm/℃ and4.0 pm/με,respectively.