The government procurement in the digital sector can promote firms' digital transformation and cross-regional operations by leveraging the substantial scale of digital public demand, playing a crucial role in enhancing firms' main business performance and building a unified national market. This paper uses a research sample of Chinese A-share listed companies from 2015 to 2021 and employs text analysis and machine learning methods to identify government digital public goods procurement indicators from nearly 650000 conventional government procurement texts. It examines their impact on firms' main business performance and the underlying mechanisms. The empirical results show that government digital public goods procurement significantly boosts firms' main business performance through "digital-driven" and "resource-expansion" effects. Heterogeneity analysis reveals that this effect is more pronounced among firms with higher financialization, non-strategic emerging industries, and those located in regions with higher levels of digital financial development. Further analysis shows that cross-regional government digital public goods procurement can incentivize firms' main business operations across regions, contributing to the construction of a unified national market. However, government digital public goods procurement also intensifies the "Matthew effect" in the main business performance between firms in central cities and peripheral cities. From the perspective of policy synergy, the sequence of implementing digital procurement first, followed by digital subsidies, better improves firms' main business performance. This paper verifies the positive role of expanding public demand in the digital sector on the development of the real economy from the perspective of procurement suppliers, providing empirical reference for government procurement to support firm development and promote market integration in the digital economy era.