A CAPTCHA method executed by a CAPTCHA system is provided, comprising: receiving a CAPTCHA request comprising category information of an application service from an application server; responding to the application server with a token identifying the CAPTCHA request and a CAPTCHA image comprising a distorted advertisement word associated to the category information and a series of randomly generated and distorted characters, both the advertisement word and the characters being a CAPTCHA text intended to be typed by a user via a user equipment connected to the application server; receiving from the application server the token and a CAPTCHA answer submitted from the user equipment by the user; and verifying the token and the answer and returning to the application server a result of the verification. This provides an improved CAPTCHA system and method with better advertising effects and security.