There is an urgent need for early detection of Pancreatic ductal adenocarcinoma (PDAC). Due to high stability and tight relationship with tumor genesis and development, miRNA has been considered as a type of potential biomarkers for PDAC detection and surveillance. However, up to now, the common miRNA panel for PDAC detection is still undetermined. In order to reveal the differential miRNA expression profiles between PDAC patients(P group), chronic pancreatitis patients(C group) and healthy persons(H group), plasma samples were collected from threegroups, further the genome wide small RNA expression profiling was performed. Overall design: Plasma miRNA samples were extracted from three groups respectively, each group 5 samples. miRNA profiles were investigated by second generation small RNA sequencing, we used CAP-miRSeq algorithm for a comprehensive analysis of small RNA sequencing reads to identify, annotate and quantify miRNAs according to the user guide with some modifications.