Desilication demanganization method at same time of preprocessing hot metal

The invention relates to a method for hot metal pretreatment and desiliconization as well as demanganization at the same time. The method comprises the hot metal pretreatment, wherein, eluant gas is utilized to spray desiliconization and demanganization agent into hot metal by adopting a powder injection method; a changing basicity method is adopted during the process of desiliconization and demanganization treatment; the SiO2 generating speed in the desiliconization reaction is calculated according to the total desiliconization amount and treatment time; the desiliconization slag basicity iscalculated, and the calculating process thereof comprises the following steps: the powder injection treatment time of desiliconization and demanganization is evenly divided into N stages, wherein, N is an integer, and N is more than or equals to 1 as well as less than or equals to 5; at the stage of N, the powder injection rate is adjusted to lead the desiliconization slag basicity in the time segment to satisfy the formu