A new test method of atmospheric visibility is proposed.This scheme improves the traditional structure of the transmission-type instrument and the scattering-type instrument.It uses reflectors to achieve round-trip-type transmission measurement and it uses displacement regulator to achieve differential measurement of atmospheric extinction coefficient.By this way,the designed system has its distinctive advantages such as strong ability to resist contamination and adjustable sensitivity for different measurement.Detailed theoretical analysis of the system is made.At the same time,structure design,optic elements selection and accuracy estimation are also carried out.That lays the foundation for a practical project.