A heat dissipating system and a power cabinet are provided. The heat dissipating system includes a cabinet, a first circulating fan and a heat exchanger. The cabinet has an outer circulating air duct and a sealed inner circulating air duct. The air inlet and the air outlet connected to the outside are arranged in the outer circulating air duct, and the heat exchanger is arranged in the cabinet and configured to exchange heat between the inner circulating air duct and the outer circulating duct. The first circulating fan is arranged outside the air inlet of the outer circulating air duct or arranged inside the outer circulating air duct, and configured to supply air to the outer circulating air duct. The heat dissipation efficiency of the inner circulating air duct is improved.