Digital factors, as a new type of production factor, are permeating various industrial sectors rapidly. They provide powerful momentum for urban economic growth and profoundly reshape the spatial structure of economic development, thereby playing a significant role in promoting coordinated regional development and narrowing the development gaps between urban and rural areas as well as among cities. Drawing on the Statistical Classification of the Digital Economy and Its Core Industries (2021) and employing input-output analysis, this paper measures the integration of the digital and real economy in various cities, aiming to examine the impact of digital factor inputs on the convergence of urban economic growth and its underlying mechanisms. The findings reveal that digital factor investment generates a notable spatial spillover effect, effectively promoting convergence in urban economic growth. It raises the speed of absolute convergence and conditional convergence by 15.74% and 4.83%, respectively, and exerts heterogeneous influences on club convergence in cities with different geographical locations, administrative tiers, and resource endowments. Mechanism tests confirm that digital factors produce spatial effects primarily through two channels: (1) breaking down regional barriers and administrative monopolies, thereby mitigating market segmentation and facilitating the freer flow and optimal allocation of production factors across broader areas; (2) accelerating the cross-regional dissemination and diffusion of advanced technologies, thereby lowering the costs of technology acquisition and application and fostering the sharing of innovation outcomes among cities. Further analysis distinguishing types of digital factors shows that inputs in digital products and services, digital technologies, and software contribute more to urban economic growth convergence than investments in digital infrastructure hardware. This paper addresses the efficiency and equity issues in the development of the digital economy from an urban system perspective and offers policy insights into leveraging the spatial effects of digital factor inputs to promote balanced regional development.