NOVELTY - Preparing clopidogrel intermediate alpha -bromo-o-chlorophenylacetic acid or its methyl ester, comprises brominating o-chlorophenylacetic acid or methyl o-chlorophenylacetate using mixture of bromide and bromate or mixture of bromide and bromic acid or mixture of bromide, bromate and bromic acid in an acidic environment under effect of ultraviolet or visible light, where the acidic condition is maintained by using an acid, bromide is hydrobromic acid and/or hydrobromide, and bromate is sodium bromate, potassium bromate, lithium bromate, magnesium bromate, calcium bromated and/ ammonium bromate.    USE - The method is useful for preparing clopidogrel intermediate alpha -bromo-o-chlorophenylacetic acid or its methyl ester.    ADVANTAGE - The method: utilizes raw materials, which are easy to store and transport; has mild reaction conditions and short reaction time; avoids usage of highly toxic brominating agent; is environment-friendly; and produces high-purity product with good yield.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) preparation of clopidogrel intermediate methyl D-(+)- alpha -(2-thienylethylamino)- alpha -(2-chlorophenyl)acetate hydrochloride (I), comprising (a) condensing alpha -bromo-o-chlorophenylacetic acid or its methyl ester and 2-thienyl-ethylamine to obtain racemic methyl alpha -(2-thienyl-ethylamino)- alpha -(2-chlorophenyl)acetate (II), (b) resolving (II) using L-tartaric acid or D-camphorsulfonic acid to obtain methyl D-(+)- alpha -(2-thienyl-ethylamino)- alpha -(2-chlorophenyl) acetate L-tartrate (III) or methyl D-(+)- alpha -(2-thienyl-ethylamino)- alpha -(2-chlorophenyl)acetate D-camphorsulfonate (IV), and (c) re-dissolving (III) or (IV) to obtain (I); and    (2) preparation of clopidogrel, comprising either brominating o-chlorophenylacetic acid or methyl o-chlorophenylacetate directly or indirectly to obtain alpha -bromo-o-chlorophenylacetic acid or its methyl ester, and reacting obtained compound with 4,5,6,7-tetrahydro-thieno(3,2-c)pyridine to obtain racemic clopidogrel, or condensing alpha -bromo-o-chlorophenylacetic acid or its methyl ester with 2-thienyl-ethylamine, and splitting into salt to obtain methyl D-(+)- alpha -(2-thienyl-ethylamino)- alpha -(2-chlorophenyl)acetate hydrochloride, and then reacting with formaldehyde obtain clopidogrel.