The invention relates to a preparation method of carbonated silicon-containing hydroxyapatite (CSi-HA) nano powder through ultrasonic coprecipitation, which comprises the following steps of: adjusting the pH value of a carbon source Ca(OH)2 to 10.5-11.5, maintaining stronger basicity and adding a phosphorus source, i.e. an H3PO4 solution, at constant temperature under the continuous action of ultrasonic waves to produce nascent state HA colloidal fluid with high purity and high dispersion degree; then, preparing a silicon source, i.e. Na2SiO3, and a carbon source, i.e. Na2CO3, in proportion into a mixed solution, continuing adding into the nascent state HA colloidal fluid at constant temperature under the continuous action of ultrasonic waves; and subsequently and continuously acting for certain time. The substitution of PO4<3-> with CO3<2-> and SiO4<4-> is effectively realized by using ultrasonic chemical action, and the carbonated silicon hydroxyapatite (CSi-HA) nano powder with high purity is obtained.