Despite growing evidence supporting the positive impact of safety investment on safety performance, little is known about how safety investment impacts safety performance in construction sites. We still need to better understand the causal relationship between safety investment and safety performance. To address this need, this article examines the ways in which safety investment impacts the safety performance of building projects. This study was conducted by means of structured interviews with project managers or safety officers of building projects. The survey results show that both direct and indirect relationships are found between safety investment and safety performance. Part of the effects of safety investment on safety performance is mediated by safety culture. A graphic model is proposed to describe the causal relationship between safety investment, safety culture and safety performance. The findings of this study contribute to a better understanding of the role of safety investment in determining the safety performance of building projects.