The present invention relates to a method for preparing a spherical powder filler, comprising steps of: S1, providing spherical siloxane having components of a 0-10 wt% unit Q and a 90-100 wt% unit T; S2, performing heat treatment on the spherical siloxane to enable silicon hydroxyl in the spherical siloxane to undergo condensation, thereby obtaining condensed siloxane; and S3, adding a treating agent to perform surface treatment on the condensed siloxane, thereby eliminating the silicon hydroxyl in the condensed siloxane to obtain a spherical powder filler. The additive amount in percentage by weight of the treating agent is 0.5-50 wt%, and the treating agent comprises a treating agent generating a unit D and/or a unit M. The present invention further provides the spherical powder filler obtained by using the preparation method, and further provides an application of the spherical powder filler. The filler provided by the present invention has a low permittivity, a low dielectric loss, no conducting impurity, no coarse particles, and a low radioactivity.
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