Objective Magnetic resonance imaging （ MRI ） was used in patients with cerebral ischemic penumbra,to analyze the coincidence of MRI findings and the patients＇condition,thus to explore the clinical value of diffusion-weighted MRI imaging in the diagnosis of cerebral infarction .Methods 104 patients with primary cerebral infarction were selected as the research subjects , they received the basic diffusion-weighted MRI imaging and diffusion-weighted magnetic resonance imaging （ DWI） scans to analyze the apparent diffusion coefficient and apparent diffusion coefficient ratios of the central area of the sick side lesion , ischemic penumbra , contralateral mirror area . Results The apparent diffusion coefficient of the central area of the lesion , contralateral mirror area , the ischemic penumbra,contralateral mirror area of ischemic penumbra were （3.783 ±1.032） ×10-4,（7.992 ±0.828） ×10 -4, （6.588 ±0.717） ×10 -4 ,（8.292 ±2.046） ×10 -4;apparent diffusion coefficient of ischemic penumbra was reduced to a certain extent ,the apparent diffusion coefficient of the central area of the lesion was reduced to a large extent ,the change was more obvious .In patients with prevalence 〈6 hours,the apparent diffusion coefficient ratios of the central area of the lesion,the ischemic penumbra were （43.4 ±10.3）,（67.9 ±3.8）; those in patients with prevalence of 6-24 hours were （50.3 ±10.5）,（76.8 ±8.7）; those in patients with prevalence of 24-64 hours were （57.2 ± 11.5）,（86.3 ±7.4）.With the prolong of sick time,the apparent diffusion coefficient ratio gradually increased ,the apparent diffusion coefficient ratio of hyper acute and acute ischemic penumbra was significantly higher than that of the central area of the lesion .Conclusion MRI combined with the application of the apparent diffusion coefficient and apparent diffusion coefficient ratio to reflect the condition of patients with cerebral infarction and predict position of ischemia penumbra have a great supporting role ,it can improve the survival rate of patients with cerebral infarction to a large extent,and provide an accurate basis for the treatment .