Aim. This study attempted to investigate the diagnostic value of interleukin-18 (IL-18), matrix metalloproteinase-9 (MMP-9), high-sensitivity C-reactive protein (hs-CRP), and fibrinogen (FIB) in acute coronary syndrome (ACS) and their correlation with the degree of vascular lesions. Materials and Methods. Altogether 206 patients with coronary heart disease admitted to our hospital were selected as research objects, including 136 patients with ACS (group A), 70 patients with stable angina pectoris (SAP) (group B), and 60 patients with noncoronary heart disease who had normal coronary angiography during the same period were selected as group C. The levels of IL-18, MMP-9, and hs-CRP in the serum were detected by enzyme-linked immunosorbent assay (ELISA), and the level of FIB in plasma was detected by automatic coagulation analyzer. Results. Serum IL-18, MMP-9, hs-CRP, and plasma FIB levels in group A were significantly higher than those in group B and group C (
p
<
0.05
). ROC curve and multivariate logistic regression showed that the sensitivity and specificity of combined diagnosis of ACS with serum IL-18, MMP-9, hs-CRP, and plasma FIB were 86.03% and 95.71%, respectively. Serum IL-18, MMP-9, hs-CRP, and plasma FIB were positively correlated with Gensini grading (
p
<
0.001
). Serum IL-18, MMP-9, hs-CRP, and plasma FIB levels were positively correlated (
p
<
0.001
). Conclusion. The combined detection of serum IL-18, MMP-9, hs-CRP, and plasma FIB has good diagnostic value for ACS, and these index levels are positively correlated with the degree of vascular lesions.