Low resistance backflow preventer is widely concerned and praised by the industry, because it can effectively solve the problem of backflow pollution of water supply system, and has the advantages of good sealing performance and small pressure loss. The structure characteristic and working principle of low resistance backflow preventer are introduced in this paper. The pressure loss test of LHS743X-16Q DN100 backflow preventer is carried out by using valve flow resistance device. The test result is qualified and its low resistance characteristic is verified. The flow field distribution is numerically simulated under the condition of fully open backflow preventer and different flow velocity. From the velocity distribution cloud diagram, it is observed that the main medium in the middle chamber presented S-type flow, and from the pressure distribution cloud diagram, it is observed that the pressure is mainly divided into two check discs and presented a three-section distribution. By comparing and analyzing the test results and simulation results, it is concluded that the working process of the backflow preventer is basically open, and the feasibility of the numerical simulation method is verified, which provides an effective reference for the structural design and optimization of the backflow preventer.