Intensity data acquired by terrestrial laser scanner contains physical and chemical information of objects. The mechanism by which the intensity data are produced is the key point to the analysis and application of intensity data. The working characteristics of terrestrial laser scanners are analyzed, hypotheses are proposed, and the calculating formulation of intensity data is simplified. The conclusion is drawn that reflectivity, incidence angle and range are the three main variables affecting the intensity data mostly. Based on a vertical surface, the distances between adjoined scanning points and influence of angular step width are analyzed and a formulation is proposed to measure a nonuniform distribution of scanning point. By simulating the intensity data of the vertical surfaces, the proposed formulation about intensity data is verified and the influence of the three variables is analyzed.