Because of their particle-reactive properties, radiogenic thorium isotopes in oceanic waters have been used in studies for the particle removal processes. In particular, 234Th has extensively been utilized to determine the carbon export flux from the euphotic zone. On the other hand, 230Th in seawater has so far mainly provided information on residence times, settling velocities and adsorption-desorption rates of 230Th in the water column. Here we introduce a new model to calculate the carbon export flux from vertical 230Th profiles. According to this model, the carbon export flux is directly related to the POC/230Th ratio in sinking or suspended particulate matter. The carbon export flux can be directly calculated from vertical profiles of POC and particulate 230Th, which should become an effective means to constrain ocean biogeochemical models.