1. A peer-to-peer networking method for integrating heterogeneous social networks, applied in a server device, comprising: connecting with a plurality peer nodes, each of the peer node defining a user end and accessing at least one social network; and the server device analyzing a directional social relationship between any two of the peer nodes according to a social relationship of the social networks, a social activity and a weight of the social activity in a time period, so as to provide a social frequency having directivity and weight, the server device further relating the corresponding peer nodes which has interactive-direction relationship and the social frequency meets a threshold value for integrating a peer-to-peer social network (P2P-iSN) which decides an effective social relationships among the peer nodes from the different social networks; wherein the server device analyzes a social strength of the social relationship between the user peer nodes so as to determines the effective social relationship, or analyzes the social strength of elated peer nodes in a set of the social relationships between the two user peer nodes with indirect relationship to determine the effective social relationship; then the server device provides interaction between the two user peer nodes; wherein the social frequency is expressed as following equation: f ⁡ ( a , b ) = ∑ i = 1 C ⁢ ⁢ w i ⁢ λ i wherein, f(a,b) denotes the social frequency of directional social relationship user a→user b, w i denotes the weight for the ith kind of activity, C denotes kinds of social activities, λ i denotes frequency that the user a performs the ith kind of activity with the user b.