The invention discloses a webpage tampering detecting method. The method comprises the steps that a proxy server obtains response webpages aiming at an access request; the proxy server inserts tempered detection scripts in the webpages; the webpages are sent to a client-side browser sending out the access request; the browser executes the tampered detection scripts and detects whether the webpages are tampered or not; the webpages are reported to a detection server if the webpages are tampered. According to the technical scheme, the webpage tempering detecting method solves the problem that in the prior art, efficiency is low due to the fact that a uniform webpage tampering detection server detects in a centralized mode, and the flexibility problem caused by the reason that tampered detection scripts need inserting into each webpage respectively, and greatly improves webpage safety on the condition of not influencing a user to access the webpages.