The invention discloses a method for determining optimal decommissioning time of power grid equipment based on three-parameter Weibull distribution. The method comprises the following steps: establishing an equipment failure rate model based on a Weibull distribution principle; carrying out parameter estimation on the failure rate model to obtain a failure rate function; and determining the optimal decommissioning time of the equipment according to the failure rate function. Compared with the prior art, the method disclosed by the invention has the advantages that 1, the method has the universality; 2, compared with a two-parameter Weibull distribution mode, the three-parameter Weibull distribution mode has a stronger capability of fitting various types of experimental data and particularly has a higher fitting precision for power grid equipment with loss failures characteristics, so that the actual condition of the failures of the equipment can be reflected well; 3, the relatively-accurate optimal decommissioning time of the equipment can be provided so that a scientific and quantitative definition standard is provided for formulating an asset entire life-cycle management policy (particularly an operation and maintenance policy and an decommissioning policy); the value of the equipment is developed sufficiently, and the energy source waste and the economic losses are reduced.