A Monte Carlo method for holistically simulating optical coherence tomography (OCT) has been developed. The geometrical optics implementation of OCT probe optical system was combined with Monte Carlo simulation for photon propagation in homogeneous turbid media to simulate OCT signal. The hyperboloid model to describe Gaussian beam's photon propagation made the simulation more accurate, and the importance sampling method has been used to accelerate the simulation process. We made the experimental measurements and simulations for Intralipid™ samples with different concentrations. Both the measured and simulated results show that the high scattering coefficient and weakly forward scattering are the primary causes for the attenuation of OCT signal as the focusing depth increases, and the OCT imaging resolution also decreases with the increase of focusing depth. The focusing plane curvature caused by scanning the fibretip laterally near the front focal plane of the OCT probe optical system deforms the OCT image and results in the decrease of image resolution also. It is also found that the effect of the numerical aperture (NA) of the fibretip on OCT signal depends on the value of NA. For a given OCT probe optical system, there is a best numerical range for NA.