Impacted by factors of aging population，system design and exectution，the sustainability of social insurance system faces grave challenges. Taking urban and rural basic pension insurance as an example，several measurements show there will be a huge gap in the annual collection if existing parameters are adopted in the operation.The sustainability of social insurance system will be a question. It also demonstrates that the reform on the collection system should be based on the effectiveness of the collection.According to analysis，there will be six advantages if taxazation authorities take full responsibility in the collecting：firstly，taxazation authorities excel in the collection and management and are proficient in information processing. Collection and management of social insurance by taxazation authorities can facilitate the realization of “full collection in accordance with law”from enterprises. Secondly，taxazation authorities across the country use the same core module in the information system，and can provide the insured efficient service. Thirdly，taxazation authorities taking full responsibility in the collecting has maginal cost advantage in collection and management. Forthly，it can press ahead the reform on social insurance system. Fifthly，it can consolidate government's responsibility in social security and push forwand the development of social insurance in an all-round effort.Sixly，it helps advance the modernization of social insurance fund governance system and government governance system.At the same time，there are also four major advantages for social insurance agencies to collect social insurance contribution.First，it can take full advantage of the professional management business. Second，it is conducive to the long-term construction of the social security system. Third，it can establish an efficient and convenient social security public service system. Fourth，it is conducive to the construction of the social security fund investment management system. Based on the analysis of the advantages and disadvantages of the two collection agencies，this report proposes some suggestions.