Reservoir architecture is currently in the stage of development，and subsurface reservoir architecture is highly dependent on well logging data, so well deviation trajectory is of great significance to it. Based on calculation of well deviation trajectory, this paper proposes the formula of true thickness of reservoir architecture unit，taking the 4th（or 5th）reservoir architecture unit in Maill’s classification as study object. Studies have shown that well deviation trajectory would be misleading to identify all levels of reservoir architecture unit’s top or bottom surface and make the calculation results of reservoir architecture unit’s true thickness too large or too small in four different modes, including horizontal reservoir architecture unit, horizontal reservoir architecture unit when well deviation trajectory drill through fault, inclined reservoir architecture unit when its inclination is opposite with well deviation trajectory’s inclination, inclined reservoir architecture unit when its inclination is same with well deviation trajectory’s inclination; well deviation trajectory also brings about the wrong understanding of effective thickness and distribution of oil and water of the reservoir architecture unit. In order to grasp the reservoir architecture in different levels accurately, it is necessary to take into account of the impact of the well deviation trajectory step by step, from rough to detailed, and ultimately to provide effective guidance for later period of oilfield development.