The ultra-lightweight block cipher PFP based on Feistel structure is suitable for extremely resource-constrained environments such as internet of things terminal devices. Up to now， the best impossible differential cryptanalysis of PFP is to use 7-round impossible differential distinguishers to attack the 9-round PFP， which can recover 36-bit master key. The structure of PFP was studied in order to evaluate the ability for resisting impossible differential cryptanalysis more accurately. Firstly， by analyzing the differential distribution characteristics of S-box in the round function， two groups of differences with probability 1 were found. Secondly， combined with the characteristics of the permutation layer， a set of 7-round impossible differential distinguishers containing 16 impossible differences was constructed. Finally， based on the constructed 7-round impossible differential distinguishers， 40-bit master key was recovered by performing impossible differential cryptanalysis on the 9-round PFP， and an impossible differential cryptanalysis method for 10-round PFP was proposed to recover 52-bit master key. The results show that the proposed method has great improvement in terms of the number of distinguishers， the number of cryptanalysis rounds， and the number of bits of the recovered key.