To explore the means of achieving carbon intensity targets in China, this study empirically discusses the key factors influencing the CO2 emission intensity and the causal relationships among these factors based on a path analysis using panel data. Six factors are included in the analysis: gross domestic product (GDP) per capita (A), technology effect (TE), energy price (EP), industrial structure (IS), energy structure (ES) and foreign direct investment (FDI). The study period is divided into three stages: 1991-2002, 2003-2014 and 1991-2014. Improving T is the most significant way to decrease the emission intensity, followed by FDI. In each stage, the effects of A, EP, ES and FDI on the emission intensity mainly come from indirect contributions through TE and IS, and the effects of TE and IS arise primarily through direct contributions. Improving A promotes the development of TE in each stage and the adjustment of IS in 1991-2002 but increases the proportion of secondary industry in 2003-2014. A rising EP negatively affects TE in 2003-2014. Improving the FDI promotes the development of TE in each stage but is not conducive to the adjustment of IS in 2003-2014.