Retrieval of ancient DNA (aDNA) sequences from organism remains provide direct view of their evolutionary history. However, researches on aDNA have suffered from lots of technical problems. Specifically, discredited sequences were generated from damaged aDNA templates, and expensive and time-consuming methods were employed. Here, a method which could recover the endogenous aDNA as well as to reduce the cost and research period is described. This is achieved by improving the ancient DNA extraction method of isopropanol precipitation, and reevaluating the method of PCR after N-glycosylase (UNG) treatment, which could remove the damaged DNA from the aDNA extract. The efficiency of these methods were tested by comparing with traditional methods using ancient specimens of pig teeth aged between 4 300 years before present (BP) and 3 900 BP. The results showed that: firstly, the extraction efficiency of the improved method of isopropanol precipitation and current method with silica-based spin column were all 60%. Furthermore, the research period at least could be reduced by half with the application of the improved methods and the cost to 1/10 of the current method. Secondly, sequences obtained through the method of PCR after UNG treatment were 100% authentic. In contrast, 66%～88% sequences were authentic based on the results obtained with the method of multiple PCRs without UNG treatment. And the research cost and period needed by the method with UNG treatment were only half of the later one. These results demonstrate that the improved extraction method of isopropanol precipitation combined with the method of PCR after UNG treatment could increase the success rate of authentic DNA amplified and at least reduce the research cost and period by half. Therefore, this method can be applied in the large-scale detection of ancient specimens.