The invention discloses a method for predicting volume shrinkage of a cavern in a salt-cavern underground gas storage, and belongs to the technical field of underground space. The method comprises: obtaining actual volume shrinkage of the cavern for n consecutive years; establishing a GM(1,1) prediction model group in combination with a grey theory according to the actual volume shrinkage of the cavern for n consecutive years, wherein the GM(1,1) prediction model group comprises m GM(1,1) prediction models; determining volume shrinkage of the cavern for n consecutive years by adopting a first GM(1,1) prediction model, obtaining n prediction results, establishing a Markov prediction model, and predicting a state of volume shrinkage in next year; determining an average value of volume shrinkage prediction values of the GM(1,1) prediction model group in the next year; and according to the average value and the state of the volume shrinkage, determining the volume shrinkage in the next year. According to the method, the volume shrinkage in the next year is predicted, so that the frequency of measurement by using a cavern sonar is reduced and the leakage risk due to sonar detection under pressure is lowered.