The propose is to explore the degradability and degradation rate of single polylactic acid chain on the single molecule level and make polylactic acid materials better used in the field of biomedicine. In this paper, by using atomic force microscopy, the single-molecule force spectroscopy of one single polylactic acid chain in water, acid and alkaline solutions are studied at the nanoscale. Based on the analysis of the single chain stretching results, it is found that the single polylactic acid chain is less likely to be hydrolyzed and broken in pure water in a short time, and but also maintain its original long chain and intrinsic elasticity. However, when it is in acid or alkaline environments, the accelerated hydrolysis behavior caused by acid or alkali environment will take place in a short time, which makes the long polylactic acid chain hydrolyze into many short polylactic acid chain fragments in a short time. It is proves that the change of the micro-environment play an important role in the accelerating hydrolysis process of polylactic acid chains on the single molecule level.