Driven by the "new infrastructure" strategy, the civil engineering industry is undergoing a profound digital transformation, which brings both opportunities and challenges for the employment of graduates majoring in civil engineering in colleges and universities. Based on a follow-up survey of graduates majoring in civil engineering from the 2023 to 2025 cohorts at University A, this paper adopts a quantitative analysis method combining frequency statistics and the entropy weight method to rank the influencing factors of employment difficulties by importance and set their weights, clarifying the quantitative impact of each factor. The research results show that factors at the students' perceptual level, such as fierce employment competition and lack of practical experience, are the core inducements of employment difficulties, while the misallocation of human capital investment, labor market segmentation, and the conflict between individual professional values and industry realities constitute the underlying mechanisms. Accordingly, this paper proposes a systematic approach centered on curriculum system reconstruction, deepened industry-education integration, dynamic assessment guarantee and upgraded employment services, and constructs a quadruple collaborative "employment ecosystem community" model involving universities, enterprises, governments and students. This model enables targeted resolution of the underlying mechanisms, and facilitates the leap of college graduates from "full employment" to "high-quality employment".