High deflection efficiency is one of the urgent requirements for practical liquid crystal computer spinner optical phased array (LC-OPA).In this paper, we demonstrate that high order grating lobes induced from fringe effect are the most important issue to reduce occupation of main lobe.A novel theoretical Pump Accessories:Hydraulic Pumps model is developed to analyze the feature of grating lobes when the device of LC-OPA is working on the scheme of variable period grating (VPG) or variable blazing grating (VBG).Subsequently, our experiments present the relevant results showing a good agreement with the theoretical analysis.