The preparation and microwave absorbing behavior of micrometric silica modified platelet iron particles (SMPLIP) were investigated. Through precipitation, hydrothermal reaction, silica modification and reduction with hydrogen, micrometric porous SMPLIP were yielded. The permittivity values of SMPLIP had been significantly decreased due to the presence of silica. Measurements and calculations showed that a 1.93mm thick sample containing SMPLIP as much as 60%by weight was capable of absorbing X band(8.2~12.4GHz) microwaves with reflection loss being greater than -10dB within the frequency range of 8.2~11.36GHz, while the maximum reflection loss was -14.8dB at 9.4GHz. The results had also shown that it was practicable to prepare thin, light weight microwave absorbent with SMPLIP.