An 
online payment system and a 
secure authentication method, including a customer, a merchant and a 
payment gateway connected over Internet; said 
payment gateway is responsible for 
processing payment information from the network, authenticating identities of the customer and the merchant and validating the validity of transaction; after a 
processing system in the 
payment gateway confirms the transaction is valid, said 
payment gateway sends a payment request and informs the two parties in the transaction of the payment information after the payment is accomplished; an assistant customer identity 
authentication system is arranged between the 
payment gateway and the customer, which connects the customer to the payment gateway in a non-Internet approach; the payment gateway generates an 
authorization code dynamically and transfers it to the customer via the assistant customer identity 
authentication system; the customer enters the 
authorization code on correct page in the payment gateway to pass identity 
authentication. The authentication method and the 
payment system greatly reduce the possibility that online data is stolen, by using both Internet and non-Internet authentication mode, and thereby improves security of 
online payment and delivers flexibility and convenience.