The invention relates to a security chip of a telephone POS (point of sale). The security chip mainly comprises a payment security module, a telephone function interface and a universal peripheral interface, wherein the payment security module comprises an on-chip CPU (central processing unit). An AHB (advanced high-performance bus) connected with the CPU is used for extending a device with a high-speed bus. An APB (advanced peripheral bus) connected with the CPU is used for extending a low-speed peripheral. An encryption and decryption unit connected with the AHB is used for encryption and decryption computing. A storage unit is connected with the AHB. A data protection unit connected with the AHB is used for storing information of security data under protection. A physical security unit connected with the AHB is used for defending various physical attacks. A bank card interface connected with the APB is used for supporting reading of back card data. The universal peripheral interface connected with the AHB or the APB is used for connecting a universal peripheral. The telephone function interface connected with the APB is used for supporting related functions of telephone payment. Payment security and telephone functions are integrated to provide a solution to a single chip of the telephone POS, which supports the payment security, and the security chip is highly safe, highly integrated, low in power consumption and cost and the like.