A Window covering cutter has its base board installed with a first clamping device for clamping a Window covering, and a knife device that is positioned next to the first clamping device, having a cutting opening, a driving plate movably fixed at a side of the cutting opening, and a knife fixed on the driving plate to reciprocate transversely to cut the Window covering. A measuring device is set at one side of the knife device for stably positioning the Window covering and measuring a length between its blocking plate and the cutting opening, providing a swift and precise measurement for cutting. So, the invention can be easily operated to esthetically cut a Window covering.