The present invention relates to an optical analysis device using a multi-light source structure, which allows acquisition of an optimized measurement result by adjusting the number of light sources depending on a concentration of an object to be measured, such as ocean spilled oil, etc., and a method therefor. The optical analysis device using a multi-light source structure may comprise: a multi-light source unit including multiple light source units each having a light source which is selectively illuminated, in order to adjust an amount of light depending on a concentration of an object to be measured; a cuvette unit including a cuvette in which an object to be measured is disposed, wherein the cuvette has a prism shape and has as many faces as the number of the light source units plus one, the light source units faces the faces, respectively, and reactive light generated from the object to be measured is emitted through the remaining one face; a light sensor unit for detecting the reactive light emitted through the cuvette; and a control unit for controlling illumination of the light source units configuring the multi-light source unit.