Objective To study the correlation between the detection of yolk sac by transvaginal sonography and serum levels of human chorionic gonadotropin (beta-HCG) in ectopic pregnancy. Methods The serum beta-HCG levels in 109 cases of ectopic pregnancy and normal controls were detected. According to the presence of yolk sac bag piece display in ectopic pregnancy, the patients were divided into two groups, the serum beta HCG levels and yolk sac bag piece diameter in two groups were observed. Results There were 59 cases of patients showed the yolk sac among 109 patients. The serum beta-HCG levels in patients with yolk sac were significantly higher than that of control group. Conclusion The serum free beta-HCG levels in ectopic pregnancy patients with yolk sac are abnormal, and the determination of beta HCG is conducive to early prevention of adverse pregnancy outcomes.