A porous membrane with dry magnetic particles dispersed therein. The pore size of the porous membrane is greater than the particle size of the magnetic particles; and the porous membrane is obtained by freeze-drying the porous membrane loaded with a buffer solution with magnetic particles evenly dispersed therein. Further disclosed is a test box containing the membrane and a preparation for the membrane. The porous membrane can enable the biochemistry properties of the magnetic particles to be maintained for a relatively long time of storage after freeze-drying, can also avoid the problem of agglomeration resulting from precipitation when storing in a liquid suspension or difficulty in performing homogeneous suspension and dispersion again.