Abstract: Objective To detect plasma homocysteine (Hcy) levels in patients with acute ST segment elevation myocardial infarction (STEMI), explore the relationship between Hcy level and no-reflow phenomenon after primary percutaneous coronary intervention (PPCI), and analyze the possible mechanism influencing its occurrence and development. Methods The basic clinical data, laboratory test results, data of coronary angiography and primary interventional therapy of 113 acute STEMI patients treated with PPCI in our hospital from April 2016 to April 2018 were retrospectively analyzed. The no-reflow phenomenon during the operation was observed in 33 patients, and blood flow was normal in the others 80 patients. Meanwhile, the plasma samples of the patients were collected to test the level of Hcy. The possible metabolism that Hcy leads to no-reflow phenomenon was analyzed statistically. Results The plasma levels of Hcy, NLR and CRP in patients with normal blood flow were all lower than those in the group with no-reflow, while there was no apparent statistical difference in traditional danger factors such as occurrence of hypertension, diabetes and cholesterol level. Conclusion The Hcy level in plasma is associated with the occurrence of no-reflow phenomenon during PPCI in acute STEMI patients. Hcy level in plasma of the NRF group is higher than that of normal blood flow group, meanwhile NLR and CRP level is higher too in NRF group; so the pathogenesis of NRF in acute STEMI after PPCI may be related to the inflammatory response associated with NLR and CRP.