Disclosed is an automatic authentication processing method and system using a dividing function. An authentication processing method performed by a computer-implementing service server comprises the steps of: (1) receiving, from a first electronic device, a service subscription request including user identification information and device information of the first electronic device; (2) requesting and receiving a one-time password (OTP) from an authentication server according to the service subscription request, wherein a first divided OTP and a second divided OTP, which are obtained by dividing the OTP, are received; (3) in response to the service subscription request, storing the first divided OTP together with the user identification information and the device information, and transmitting the second divided OTP to the first electronic device; and (4) in a case of a service requiring authentication for the user identification information, transmitting the first divided OTP together with the second divided OTP received from the first electronic device to the authentication server so as to perform authentication processing.