Aim To investigate the associations of methylenetetrahydrofolate reductase(MTHFR)gene C677T polymorphism and levels of plasma homocystein and coronary heart disease. Methods A total of 256 patients admitted in our hospital from 2013 to 2015 were divided into two groups according to age:<60 years group(goung and middle-aged group, n=107) and ≥60 years group (old-aged group, n=149) . We selected 145 healthy controls as control group. The MTHFR gene C677T polymorphism was detected by polymerase chain reaction(PCR) and gene chip technology. The levels of plasma homocystein were detected by high performance liquid chromatography in all groups. We analyzed distribution of the MTHFR gene C677T polymorphism and the levels of plasma homocystein in all groups. Results The frequency of CC(homozygous normal),CT(heterozygous),and TT(homozygous mutant) in group <60 years, ≥60 years, control was individually 26.2%,43.9%,29.9%;35.6%,42.3%,22.1% and 37.9%,40.1%,21.4%. The frequency of control group and T alleles in group <60 years, ≥60 years,control group was individually 48.1%,51.9%;56.8%, 43.2% and 58.3%, 41.7%. There was significant difference in the allele frequency of C677T polymorphism between <60 years group and control group (χ²=5.10,P=0.015). There was no significant difference between ≥60 years group and control group (χ²=0.147,P=0.382). The levels of plasma homocystein in <60 years group were higher than control group. Conclusion There was higher levels of plasma homocystein in TT genotype. There was only associations between the MTHFR gene C677T polymorphism and young and middle-aged CHD patients. There was not relationship in old-aged CHD patients. The higher levels of plasma homocystein and higher T allele frequency maybe were risk factors in young and middle-aged CHD patients. The pathogenesis of CHD was different in different age grades patients.