The invention belongs to the technical field of POS terminal security. The invention relates to a POS terminal, in particular to a PIN safety input method of a full-touch-screen POS terminal. The method specifically comprises the following steps that S1, after a terminal is started, an application CPU controls a touch screen in a default mode, and when an application program requires to execute PIN input, the application CPU informs a safety CPU and sends parameters related to PIN input to the safety CPU; s2, the safety CPU receives a PIN input request sent by the application CPU, and immediately switches the touch screen control signal from the application CPU to itself; S3, the safety CPU circularly detects and processes PIN input on the touch screen, and when PIN input is finished, a PIN secret key preinstalled by the safety CPU is used for encrypting the PIN, and then the ciphertext PIN is returned to the application CPU, and a touch screen control signal is switched to the application CPU; and S4, the application CPU packages the ciphertext PIN acquired from the security CPU into transaction data and then sends the transaction data to a transaction background, so that one financial transaction is completed.