Aims: 11C‑L‑methionine, an amino acid tracer used to delineate certain tumor tissues, has proven to be a prevailing nonfluorodeoxyglucose positron emission tomography (PET) radiopharmaceutical. We intended to prepare 11C‑L‑methionine by following modified synthetic strategies at a rebuilt working area to meet the PET drug current good manufacturing practice (cGMP) and Pharmaceutical Inspection Co‑operation Scheme (PIC/S) regulations. Furthermore, we overcame the problem of pyrogen cross‑contamination using a cleaner and more efficient program. Material and Methods: The task of upgrading air filtration equipment was integrated with the set of Web‑Based Building Automation system (WebCTRL®). 11C‑L‑methionine synthesis was carried out in accordance with redesigned methods to meet the requirements of PET drug cGMP. The product quality was tested by a series of quality control tests and was found to be satisfactory. Depyrogenation was carried out by three different methods with different flow rates and flushing durations. The results were examined through limulus amebocyte lysate clotting test. Results: The level of air cleanliness in each section meets the PIC/S GMP standards after the reconstructions. Moreover, after delicate modifications, the radiochemical yield of 11C‑L‑methionine was 36.20% ± 3.59% (based on 11C‑CH3I, n = 7), which is about 10% higher than the average former yield. Besides, the used depyrogenation methods could wipe the bioburden off within 8 h. Conclusions: The modifications done not only offer a good production environment but also protect the products from contamination. The modified approaches in both 11C‑L‑methionine production and depyrogenation resulted in prominent progress in stability and efficiency as well.