The utility model relates to a noise reduction device for an outlet side of a fan, and a heat exchange system including the noise reduction device. The noise reduction device includes: a connecting portion configured to be connected with at least a part of the air duct cover, and form an accommodation space communicating with an airflow on the outlet side via at least one of the through holes; and at least one first chamber and/or at least one second chamber, the first chamber being located in the accommodation space and filled with a sound-absorbing material, and the second chamber being located in the accommodation space and configured as a resonant noise-reduction cavity. The utility model is easy to manufacture, install and maintain, the noise reduction effect is obvious, and therefore the utility model has significant practicability.