The adhesion properties of lunar dust grains are a key to determine its motion state. Atomic force microscopy (AFM) is conducted to evaluate the adhesion properties of such ultrasmall grains. However, an efficient method to measure the adhesion properties of lunar grains has not yet been developed because of the difficulties in eliminating the effect of adsorption of water and gases on the grain surface. In this study, an improved method was proposed to measure the adhesion force of grains while effectively eliminating the gas molecule adsorption effect. In the proposed method, using a focused ion beam, a small grain was mounted onto the tip of an AFM probe then used to measure the adhesion force of the grain. To determine the effects of environmental pressure and temperature, the adhesion force between a silica ball and a silica wafer was measured under different conditions. Based on the results, the gas molecule adsorption effect can be effectively eliminated during adhesion force measurement through AFM at a temperature of 200. and an environmental pressure of <2.4 x10(-4) Pa, at which strong adhesion of the grain is achieved. The proposed method is suitable for the measurement of adhesion force in lunar grain samples.