The concept of element transition probability and the structure of internal inverse P_{ρ}-set X¯^{P_F} were proposed based on the inverse P-sets X¯^F, X¯^{F¯ and the randomness of element transition. The relationship between internal inverse P-set X¯^F and internal inverse P_{ρ}-set X¯^{p_F} was discussed, which showed X¯^{p_F } is the general forming of X¯^F while X¯^F is a special case of X¯^{p_F}. The relationship theorem between X¯^{p_F} and element transition probability, and the identification theorem between internal inverse P_{ρ}-set family and internal inverse P-set family were presented. Furthermore analysis of the probability feature about internal inverse P_{ρ}-set X¯^{p_F} was given at the end.