A security authentication method for a membership login of an online website by use of a security authentication server, the security authentication method comprising: receive a request for a security authentication for a membership login of an online website from a user terminal; generating one-time use authentication information in the form of a QR code image in response to the received request; transmitting the generated one-time use authentication information to the user terminal for display on a screen of the user terminal in the form of the QR code image for scanning and analyzing by a smartphone; receiving a request for one-time password information from a security authentication related application installed on the smartphone, the request including the analyzed one-time use authentication information and actual membership login authentication information of the online website; verifying the one-time use authentication information and the actual membership login authentication information of the online website; generating one-time password information if a corresponding user is an authenticated member; transmitting the generated one-time password information to the smartphone for display to a user and for input by the user to the user terminal; receiving a request for a security authentication for the membership login of the online website from the user terminal, the request including the one-time password information and the one-time use authentication information; and performing a verification process on the security authentication for the membership login of the online website, and if the user is a security authenticated member, normally processing the membership login of the online website. receive a request for a security authentication for a membership login of an online website from a user terminal; generating one-time use authentication information in the form of a QR code image in response to the received request; transmitting the generated one-time use authentication information to the user terminal for display on a screen of the user terminal in the form of the QR code image for scanning and analyzing by a smartphone; receiving a request for one-time password information from a security authentication related application installed on the smartphone, the request including the analyzed one-time use authentication information and actual membership login authentication information of the online website; verifying the one-time use authentication information and the actual membership login authentication information of the online website; generating one-time password information if a corresponding user is an authenticated member; transmitting the generated one-time password information to the smartphone for display to a user and for input by the user to the user terminal; receiving a request for a security authentication for the membership login of the online website from the user terminal, the request including the one-time password information and the one-time use authentication information; and performing a verification process on the security authentication for the membership login of the online website, and if the user is a security authenticated member, normally processing the membership login of the online website.