Abstract： Objective To study the safety and effectiveness of modified radioactive 125I seed implantation in treatment of lung cancer patients with poor lung function. Methods Thirty one lung cancer patients with poor lung function were enrolled into this study. All of them were implanted 125I seed with technology of fan-shaped distribution and coaxial puncture. Brachytherapy planning system(TPS) was used to draw up a preoperative implantation plan. Fan-shaped seed distribution system was used to simulate surgical program, and implantation pitch was 0.5 to 1.0 cm. Real-time adjustment is necessary during surgery. Dose distributions were checked by TPS immediately after implantation. Match peripheral dose(MPD),the dose of 90% tumor volume(D90)and the tumor volume covered by 90% prescription dose(D90)were calculated. Intraoperative and postoperative surgery-related complications were analyzed. All patients were followed up to 6 months, at month 2, 4 and 6 post-procedure, CT scan was performed to evaluate the local control rate of tumors. Results The technical success rate was 100% for placement of the 125I seed. MPD of the tumors was 90 to 140 Gy. D90 was 95 to 146 Gy,median dose was 118 Gy.V90 was 92%to 97%,median dose was 94%. Surgery-related complications included pulmonary hemorrhage(1 patient), pleural cavity hemorrhage (2 patients), pneumothorax(2 patients). The 2-month, 4-month and 6-monthlocal control rates were 31%(10/32), 78%(25/32) and 90%(29/32)respectively. The overall complete remission(CR) rate was18%(6/32), partial response(PR) rate was 72%(23/32), stable disease(SD)rate was6%(2/32), progression disease(PD) rate was 3%(1/32).Acute radiation pneumonitis Grade 0 in 29 patients, Grade Ⅰin 4 patients; advanced radiation pneumonitis:grade 0 in 30 patients and gradeⅠin 3 patients. Conclusions The technology of fan-shaped distribution and coaxial puncture for radioactive 125I seed implantation was safe and effective to treat lung cancer patients with poor lung function.