Inclusion Criteria:  Stage I lung adenocarcinoma patients underwent complete surgical resection with negative margins (R0) and harbor sensitizing EGFR mutations (exon 19 and/or exon 21). Positive ctDNA after surgery and prior to adjuvant therapy (4 weeks after surgery). Completely recovered from surgery before adjuvant treatment and showed no signs of tumor recurrence in imaging. Adequate organ function: 1) Hemoglobin ≥ 9.0 g/dL; 2)Absolute neutrophil count (ANC) ≥ 1500 cells/mm3; 3) Platelets ≥ 90,000/mm3; 4) AST, ALT ≤ 2.5 x ULN; 5) Total bilirubin ≤ 1.5 x ULN; 6) Serum creatinine ≤ 1.5x ULN and calculated creatinine clearance ≥ 60ml/min. Age >18 years old. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. Females must have a negative pregnancy test within 7 days prior to the start of dosing if of child-bearing potential. Males and females of reproductive potential who are sexually active must agree to use adequate contraception prior to entry, during the process and 8 weeks after drug withdrawal. Written informed consent. Compliance with the protocol. Ability to swallow the formulated product.  Exclusion Criteria:  Any type of systemic anticancer therapy for lung adenocarcinomas, including chemotherapy, targeted therapy or immunotherapy. Any prior local radiotherapy for lung adenocarcinomas. Clinical objective evidence (pathology or imaging) to confirm disease recurrence before the start of adjuvant therapy. Allergy to furmonertinib or any ingredients. Past medical history of ILD, drug-induced ILD or any evidence of clinically active ILD; CT scan at baseline revealed the presence of idiopathic pulmonary fibrosis. Any evidence of uncontrolled systemic diseases, including active infection, uncontrolled hypertension, unstable angina, angina within the last 3 months, congestive heart failure (≥ New York Heart Association [NYHA] Grade II), myocardial infarction (6 months before enrollment), severe arrhythmia requiring medical treatment, liver diseases, kidney diseases or metabolic diseases. Known history of human immunodeficiency virus (HIV) infection. Pregnant or lactating women. History of neurological or psychiatric disorders, including epilepsy or dementia. Other judgments by the Investigator that the patient should not participate in the study.