A secure transfer method for a cloud-based Point of Sale transaction sensitive data performed by a cloud Point of Sale background system, comprising steps of: (a) exchanging a transaction process key with a cloud Point of Sale terminal; (b) receiving, from the cloud Point of Sale terminal, a transaction request packet encrypted by using the transaction process key; and (c) obtaining a transaction sensitive data from the transaction request packet, and performing operations on the transaction sensitive data by using the transaction process key in order to upload to a financial acquiring platform; wherein the step (a) comprise: - receiving a sign-in request from a payment application in the cloud Point of Sale terminal; - based on the sign-in request, emanating the transaction process key through a transaction primary key which is recorded in the cloud Point of Sale background system, wherein the transaction primary key corresponds to the cloud Point of Sale terminal, and is manually injected into a secure module of the cloud Point of Sale terminal during the initialization of the cloud Point of Sale terminal; - generating a sign-in response packet, the packet containing the emanated transaction process key; and - sending the sign-in response packet down to the cloud Point of Sale terminal through a secure channel; wherein the step (c) comprises: - parsing the transaction request packet to obtain the transaction sensitive data; - using the transaction process key to decrypt and perform data integrity validation; and - uploading the transaction sensitive data to the financial acquiring platform in an appropriate packet format. (a) exchanging a transaction process key with a cloud Point of Sale terminal; (b) receiving, from the cloud Point of Sale terminal, a transaction request packet encrypted by using the transaction process key; and (c) obtaining a transaction sensitive data from the transaction request packet, and performing operations on the transaction sensitive data by using the transaction process key in order to upload to a financial acquiring platform; - receiving a sign-in request from a payment application in the cloud Point of Sale terminal; - based on the sign-in request, emanating the transaction process key through a transaction primary key which is recorded in the cloud Point of Sale background system, wherein the transaction primary key corresponds to the cloud Point of Sale terminal, and is manually injected into a secure module of the cloud Point of Sale terminal during the initialization of the cloud Point of Sale terminal; - generating a sign-in response packet, the packet containing the emanated transaction process key; and - sending the sign-in response packet down to the cloud Point of Sale terminal through a secure channel; - generating a sign-in response packet, the packet containing the emanated transaction process key; and - sending the sign-in response packet down to the cloud Point of Sale terminal through a secure channel; - parsing the transaction request packet to obtain the transaction sensitive data; - using the transaction process key to decrypt and perform data integrity validation; and - uploading the transaction sensitive data to the financial acquiring platform in an appropriate packet format.