VoIP which transmits voice over IP will be the basic technology carrying voice through telecom network in the future. Using the designing model of traditional call centers for reference, authors design the model and framework of VoIP call center based on H.323 and realize it through Softswitch. Compared with traditional call centers, the system designed has several advantages such as replacing costly Private Branch Exchange (PBX) with a software Softswitch, supporting both Public Switched Telephone Network (PSTN) and Internet connecting. In addition, it gets rid of the limitation of space to support distributed agents. It can transmit voice, video and instant messages, implement Text to Speech (TTS) and Automatic Speech Recognition (ASR).