As there are few engineering examples of demolition construction of long-span concrete cable-stayed bridge for reference, construction monitoring of its demolition process plays an important guiding role in whole demolition construction. Taking the concrete cable-stayed bridge with a middle span of 200m of the old bridge of Maogang bridge in Shanghai as an engineering example, this paper discusses principles of construction monitoring of the old bridge demolition, introduces main ideas and contents of structural analysis for construction monitoring, and designs an on-site monitoring system to meet the needs of bridge demolition monitoring. During demolition of the old bridge, through comparison between theoretical and measured values of main controlling parameters such as stay cable force, main tower deflection and main beam displacement, and paying attention to changes of stresses in key sections of the main tower and main beam, structural safety risk in demolition process is effectively controlled to ensure smooth demolition of the old bridge.