Carrier injection performed in Pr0.7Ca0.aMnO3 junctions demonstrate resistance switching (RS) characteristic with dramatic changes in both resistances and interface barriers,which suggests a charge carrier self-trapping model in strongly correlated electronic framework. Un-stable RS behaviour without electric fields in epitaxial Pr0.7(Ca1-xSrx)0.3MnO3 (PCSMO) films shows dependences on insulator-metal transition temperature,which indicates that RS process is really related to the intrinsic property of carriers.The switched resistance of epitaxial PCSMO films also depends on the amount of current pulses,which should be another evidence of the carrier self-trapping model,similarly to the dependence on the amount of self-trapped charge carriers.