Operation system and method of workflow are provided. The system includes a mail platform and a web application. The mail platform receives an email including an application identification of the web application, a target URL corresponding to a target, and at least one recipient. The mail platform then mails a notification email including a data processor and the email to the recipient. The data processor automatically retrieves user information of an operator if the data processor in the notification email is triggered by the operator, and transmits a message having the user information and the target URL to the web application according to the application identification. The web application authenticates the user information and launches the target according to the target URL if the user information conforms to the recipient.