The key for dynamic calculation of fan bridge of direct air-cooling system of coal-fired power plants is to determine the oscillation force of fan bridge. Based on measurement of the strain of fan shaft during fan operation, the strain curves of the fan shaft are obtained. According to the measured strain curves, the oscillation force characteristics of the fan bridge is analyzed and the calculation method of oscillation force is proposed, which can be used as a reference for . self-design of direct air-cooling system in China.