Determination of index weights in the current heterogeneous network selection algorithm is of subjectivity. To solve this, a network selection algorithm based on fuzzy Analytic Hierarchy Process (AHP) and extension theory was proposed. Based on the analysis of the network requirements of different business, and the combination of extension theory, the collected performance parameters were mapped into corresponding calibration interval. Through the establishment of the network and calculation of the relative membership degree of the matter-element, a new decision matrix was constructed. The integrated weights of the network performance parameters were calculated by fuzzy AHP. Finally, the optimal access network was chosen through the weighted ranking of the relative membership degree. The simulation results show that the algorithm can take account of the business types of different users' and network objective performance, and multi-mode terminal can select the network accurately and effectively in the heterogeneous networks.