The invention provides a method for measuring the porosity of rock debris. The method comprises: determining the first porosity of rock cores with different lithology in a block; removing a part of the rock cores to form irregular rock bodies, obtaining CT images of the irregular rock bodies, and determining the second porosity of the irregular rock bodies according to the CT images; regulating the distribution range of the pore gray value of the irregular rock bodies, and correcting the second porosity of the irregular rock bodies according to the corresponding CT images till the second porosity matches the first porosity; according to the corrected second porosity, establishing a corresponding relation between the irregular rock bodies with different lithology in the block and the distribution range of the pore gray value of the irregular rock bodies; determining the lithology of rock debris of a rock-core-free sample well location in the block, and obtaining a CT image of rock debris; according to the corresponding relation and lithology of rock debris, determining the distribution range of the pore gray value of rock debris; and according to the CT image of rock debris and thedistribution range of the pore gray value, determining the porosity of rock debris. The method allows the porosity of rock debris to be accurately obtained, and the utilization rate of a rock debris sample is improved.