Abstract: Inner wall flaws especially localized corrosion in pipe under insulation are among those most hazardous to pipelines under insulation.An inspection system is designed to detect inner wall flaws in pipe based on pulsed eddy current technique and effects of probe type on diction are studied.Test pieces with different area and depth are made to simulate localized corrosions.Three types of detection probes,circular,double-coil focusing and U-shaped focusing,are designed and manufactured.A series of experiments are performed and detection sensitivities of different probes are compared.The experiments show that U-shaped probe has the highest detection sensitivity among three types of probes while circular probe is the worst for detecting localized inner wall flaws.