My car is MB B200, when using the A/C with the closed circulation mode, I smell the smoke from outside the car. the smell from outside is not that strong, but this means that there is a leakage somewhere, from which the smell comes in.
does anyone has this experience?

I have a similar condition with my B200. It just tells me that, even with closed circulation, the passenger cabin is not hermetically sealed. It could have been done on purpose - some vehicles do allow some fresh air in even when set to closed. Or it could simply be a fit and finish problem, meaning, the vents and seals do not fit perfectly and allow outside air to seep in. Mine is negligible and doesn't bother me, though.