Above the critical micelle concentration (cmc), surfactants or their mixtures can self-assemble into a variety of aggregates such as micelles, vesicle-phase and lamellar phase etc. As one of the soft matters, amphiphilic bilayer membranes are very important in cytology, which represent simple model systems for biological membranes. Among them, the studies of bilayer membranes formed by cationic surfactants have been one of the most active areas at present. In general, when catanionic surfactants are simply mixed in water, precipitate is easily formed, especially when salt forming after two surfactants are mixed. Thus, the salts will screen the electrostatic interaction between aggregates. So a series of salt-free catanionic surfactant systems have been widely studied recently. Precipitate would not easily formed in the type of systems, and furthermore some aggregates of unique structure have been found. In this paper, we synthesized a basic surfactant with the method of ion-exchange.And we synthesized a double-tailed carboxylic acid anionic surfactant. The focus was on the system of the two surfactants mixture in aqueous solutions. A phase diagram was delineated, and the phase transition and the shape and microstruture of the aggregates were measured with obsersion throuth polarized light, conductivity measurement and obervation with TEM.