The invention discloses a circulating tumor DNA EGFR (Epidermal Growth Factor Receptor) detecting technology and a reagent kit thereof. The circulating tumor DNA EGFR detecting technology comprises the following steps: step 1, designing a synthetic primer, a closed probe and a detecting probe for a mutation site; step 2, processing a sample and extracting DNA; step 3, applying the circulating tumor DNA EGFR detecting technology to the reagent kit, and establishing a PCR amplified reaction system. According to the circulating tumor DNA EGFR detecting technology disclosed by the invention, the specific MGB Blocker probe, the EGFR specific probe and the primer are adopted to detect the EGFR mutation in the circulating tumor DNA; the MGB Blocker probe is utilized to retard nonspecific amplification of the EGFR wild type genome and improves the sensitivity; the circulating tumor DNA EGFR detecting technology can be used for detecting the EGFR mutation in the circulating tumor DNA, is simple to operate, cheap in detection, capable of being popularized at a large scale and high in detection speed; the detecting process can be completed for about 2 hours.