Photoacoustic tomography is a noninvasive and nonionized biomedical imaging modality but it cannot reveal the inner structure and sideward boundary information of blood vessels in the linear array detection mode. In contrast, Monte Carlo (MC) light transport could provide the optical fluence distribution around the entire vascular area. This research explores the combination of linear array transducer-based photoacoustic tomography and MC light transport in the blood vessel quantification. Simulation, phantom, and in vivo experiments are in good correlation with the ultrasound imaging, validating this approach can clearly visualize the internal region of blood vessels from background tissue.