This is a novel method for production of no-carrier-added O-(2-[.sup.18F]fluoroethyl)-L-Tyrosine, which has been proved a suitable PET (position emission tomography) probe for tumor diagnosis imaging, and the preparation of the title compound starts from precursors with the chemical structures as in Formula 1, wherein R.sup.1 is a protective group for the carboxyl functional group, R.sup.2 is a protective group for the amino group, and R.sup.3 acts as a leaving group, R.sup.1 represents an arylalkyl group, R.sup.2 represents a carboxyl group, and R.sup.3 represents a p-tosyloxy, methane sulfonyloxy or trifluoromethane sulfonyloxy or bromine, and the final purification of the product is using a separation column, which is very convenient for automated synthesis, and the invention uses the precursor with the chemical structures as in Formula 1.