Aim To observe the relationship between serum lipoprotein(a) [Lp(a)], β2-microglobulin (β2-MG) and tumor necrosis factor-α (TNF-α) levels and degree of coronary artery lesion in patients with acute coronary syndrome (ACS), and to analyze their clinical significance. Methods A total of 87 patients diagnosed as ACS from June 2015 to June 2018 was collected, including 54 cases of unstable angina pectoris (UA) and 33 cases of acute myocardial infarction (AMI). Another 32 healthy person with basically matched age and gender in the same period were selected as control group. The levels of serum Lp(a), β2-MG and TNF-α were detected in all subjects, and the relationship between their levels and degree of coronary artery lesion was analyzed. Results Compared with control group, serum levels of Lp(a), β2-MG and TNF-α in ACS patients were increased significantly (P＜0.05), and serum levels of Lp(a) and TNF-α in AMI group were significantly higher than those in UA group (P＜0.05). With the increase of coronary artery lesion number and modified Gensini score grading, the serum levels of Lp(a), β2-MG and TNF-α in ACS patients were also increased (P＜0.05). Pearson correlation analysis showed that serum Lp(a), β2-MG and TNF-α levels were positively correlated with the number of coronary lesions and the modified Gensini score grading in ACS patients, respectively (P＜0.05). Logistic regression analysis showed that serum Lp(a), β2-MG and TNF-α levels were independent risk factors for ACS, in addition to the conventional influencing factors of ACS. Conclusions Serum levels of Lp(a), β2-MG and TNF-α in ACS patients are positively correlated with the degree of coronary artery lesions. With the disease aggravation of ACS patients, serum levels of Lp(a), β2-MG and TNF-α also rise.