The invention discloses a pipeline inner positioning device based on a pipeline section length and pipeline connector detection and a positioning method thereof, and belongs to the technical field ofpipeline mapping. The device and the method aim to solve the problems of low positioning and orienting precision of a small-diameter pipeline detection positioning system. According to the device, a main body is composed of a sealed cavity and is sequentially provided with a data storage unit, a data processing unit, an MEMS strapdown inertial measurement unit and a power supply module from left to right; and the two ends of the outer wall of the main body are symmetrically provided with a plurality of mileage wheels and supporting wheels at equal intervals, pipeline defect detection sensors are arranged on the parts, between the mileage wheels and the corresponding supporting wheels, of the outer wall of the main body, and the pipeline defect detection sensors, the mileage wheels and thesupporting wheels are isolated by plastic sealing rings. In addition, a complex continuous wavelet transformation pipeline connector is adopted in the positioning method based on the pipeline sectionlength and the pipeline connector detection, on one hand, azimuth angle and pitching angle error correction are provided for the pipeline positioning system on a straight pipeline section, and on theother hand, a pipeline section length information base is combined to provide the position error correction for the pipeline positioning system so that accurate positioning of pipeline defects can beachieved.