The invention provides an initial trimming method of an underwater towed body buffer mooring cable of a wave glider, As initial conditions sucn as that number of mooring segment, the gravity and buoyancy of parts of nodes are determined,\ , Buffer mooring cables are divided into segment groups, and the static equilibrium equations are solved for each segment group or individual segment, and then the gravity or buoyancy force that needs to be configured at other nodes is solved, and the estimation values of vertical load on the towing parent body and the angle between each segment and the horizontal plane are provided. Using the calculation result of the present invention as the initial value of a further water trimming test, It can reduce the blindness of underwater trimming test, improvethe efficiency of determining the final trimming scheme, and further provide the estimation of trimming scheme and corresponding tether shape under various initial conditions, the estimation of towedparent load, and the formation of the map, which provides the basis for scheme selection.