Radiofrequency ablation (RFA) method is an important surgery method, because of its minimally invasive feature, no need of general anesthesia, and high survival rate. However, steam-popping phenomenon during RFA method can cause metastasis to adjacent tissue, so it is still dangerous method. In present, sound signal through human ear or recording machine was used to sense the steam popping, but this method is hard to be used as driving algorithm due to its high possibility of environmental noise. In order to solve this problem, this research proposed steam-popping sensing method through attached flexible pressure sensor on RFA needle. Flexible pressure sensor need several conditions to monitor pressure change during steam popping. It should have wider pressure range than conventional flexible pressure sensor, should thin enough that it does not affect to the RFA needle insertion process, should biocompatible, and should environment-insensitive because of tough environment of human body inside. However, this flexible pressure sensor was hard to find, so the flexible pressure sensor which satisfy this condition also developed. In this research, naturally roughened polyimide/carbon nanotube (PI/CNT) film based sensor and roughness controlled PI/CNT film based sensor were fabricated and characterized. In case of the NR - PI/CNT based sensor, it shows 89.19/MPa of sensitivity in maximum, and has the pressure sensing range of 50kPa ~ 400kPa. In case of the CR - PI/CNT based sensor, it shows 35.47/MPa of sensitivity in maximum, and has the pressure sensing range of 10kPa ~ 500kPa. Both of the proposed sensors show above 75% of sensing ability of steam popping with the integration on commercial RFA needle.