The invention provides an on-line transaction card stealing rate assessment method and device. The on-line transaction card stealing rate assessment method includes the following steps: collecting card stealing data of a set historical time period and corresponding transaction data; generating a relation curve of the card stealing notification receiving rate and time according to the card stealing data and corresponding transaction data; and calculating the card stealing rate within unit statistical time according to the relation curve. By utilization of the on-line transaction card stealing rate assessment method and device provided by the application, according card stealing data returned by a bank, the recent true card stealing level can be estimated, and the overall card stealing trend of an on-line transaction platform can be assessed.