Excuse me, what focal length lens does Canon SLR match to achieve this effect of the model?

The background of this photo is not too blurred, but the aperture of 18-200 is obviously not large enough. To achieve shallow depth of field, we can rely on its telephoto end. However, if you take a full-length portrait with a telephoto end, you need to stand far away, which may be difficult to operate in practice. So I suggest you use a large aperture lens, such as the cheapest 50mm 1.8, which is a good choice. A racket is enough.

Good luck!