Through the entanglement swapping between Bell states, the relationship between the resulting state and the initial state is illustrated and utilized to design an efficient quantum secure multiparty summation protocol. In the proposed protocol, a semi-trusted third party is introduced to generate Bell states and distribute them among participants. Then according to his private data, each participant performs the corresponding encoding operations on the Bell states. Finally, all participants make Bell states measurements on the particles in their hands and achieve entanglement swapping, and the third party can calculate the summation of the private inputs based on the measurement results and the initial states. The security analysis shows that the proposed protocol is secure against external and internal attacks in theory.