Since twentieth Century 40's, some foreign enterprises in developed countries began to study and produce sweeper [1-2]. Research on China's sweeping car began in twentieth Century 60 years, but until the 80 time end when china had been reforming and opening that it began to rapidly develope [3-4].But the study of mouth has the same general trend at home and abroad. Due to the different design of suction mouth, circulation type pneumatic conveying systems in general can be divided into open pneumatic conveying system using pure suction type suction mouth [5] and the use of reverse blowing type suction mouth delivery system [6]. Now most of the sweeper adopts the latter, but if the back blowing type suction mouth design improperly ,it can not achieve the ideal effect of absorbing dust, and may lead to strong fugitive dust [7-9].Today although road sweeper have been studied for decades at home and aboard, but these studies mainly is through the enterprise using engineering practice means to complete ,there are two situations occurring as follows: a number of technical on research and development need to rely on our own to explore; The engineering practice have greater demand for human, material and financial resources, and it is difficult to achieve better expected. In order to solve the problems of the above two points, according to the fluid mechanics analysis, this paper mainly research and analyze the sweeper suction mouth's flow field pickup role of entrainment process for particulate contamination by negative pressure suction, which can provide a foundation for the research and optimization of sweeper pneumatic conveying system.