The Burnett equations with slip boundary conditions are used in present paper to investigate the flow characteristics of microfilter in slip/transition regime. Convergent results of the Burnett equations agree very well with the results of DSMC method. The difference between the results of the Burnett and the Navier-Stokes equations increases with the increase of Knudsen number. The variation of non-dimensional pressure drop with Reynolds number and the opening factor are presented. The non-dimensional pressure drop is independent of Knudsen number.