The invention relates to the field of insulation monitoring of gas-insulated metal-enclosed switchgear (GIS), and more particularly to a method and apparatus for simulating partial discharge signals at different degrees. The method comprising: presetting different GIS typical insulation defect partial discharge signal envelope diagrams and impulse source frequency signals corresponding to the four stages of the partial discharge in a microprocessor; when it is required to simulate the GIS typical insulation defect partial discharge signals at different degrees, enabling a signal envelope diagram corresponding to the defect to intercept the pulse signal in the corresponding stage to obtain the partial discharge signals at different degrees under different GIS typical insulation defects. The method and the device solve the problem that simulated different defect types and different partial discharge stage signals cannot be provided in the GIS partial discharge detection field, can provide a really simulated partial discharge signal source under different insulation defects and different degrees, solve the problem of incapability of GIS ultrahigh frequency system effectiveness detection and effectiveness degree detection, and show a huge application prospect.