As the project volume increases, the risk will increase correspondingly. In order to finish the project successfully, usually, the client would ask the contractor to submit a performance security sum. However, its meaning and form are not very clear and there is a lot of abnormal operation in China. Many dissensions have been arisen, which make the project performance difficult. Starting with a case study combined with international convention, the meaning and form of the performance security sum are explained in detail and the performance bond is introduced as a main point. At the same time, aiming at the actual situation in China some instructive advice according to international experience is put forward.