Size effect and wall effect are very common problems in seepage test of broadly graded coarse materials. A series of seepage tests are performed. The size effect is analyzed and the principle for apparatus size selection is studied. It is proposed that the apparatus diameter is not less than 6 times of test material’s d85. Effects of different methods for treating grains of size over limit on permeability test results are discussed. It is concluded that carefully taking equivalently alternative method is acceptable; while scale method is not. The wall effect is discussed and the thickness of wall treatment layer is proposed.