The invention provides a method for computing an effective seepage pore throat radius of a low-permeability sandstone reservoir. The computing method comprises the following steps: step 1, testing a capillary pressure curve of a sandstone core, so as to acquire distributed data of a micro-pore structure of the reservoir; step 2, computing a contribution rate of a single pore throat for seepage permeability according to the distributed data of the micro-pore structure; step 3, subtracting a lower limiting value of a pore throat radius from each pore throat radius, so as to acquire distributed data of an effective radius; step 4, computing the effective seepage pore throat radius according to the distribution of effective pore throat data. According to the method, the effective radius of actual seepage of the low-permeability reservoir can be quantitatively computed, so that the foundation is laid for reasonable assessing of the seepage capability and effective development of the low-permeability reservoir.