A method of preparing an oxidized starch haemostatic material, including adding a starch raw material to an external circulation pulsatile reactor; switching on a pump to allow inflow of dry air for drying the raw material; switching on a heat exchanger; vacuumizing the reactor; opening a nitrogen dioxide pipeline and a dry air pipeline; pumping in a mixed gas; controlling temperature at 0-120° C. by the heat exchanger; wherein nitrogen dioxide is contacted with the raw material to trigger a selective oxidation reaction and is continuously recycled; an airflow circulation switch is switched on and off at a pulsating ratio of 1:1-10 to carry out airflow pulsation; stopping inflow of nitrogen dioxide and continuing airflow circulation for 5-30 minutes; after completion of the reaction, adjusting to room temperature; vacuumizing the reactor and treating exhaust gas; allowing nitrogen gas to flow in for rinsing the replaced reactor until completion.