Abstract: In order to measure the accurate reflection coefficient of waveguide component at millimeter-wave band, a method for reflectometer calibration was proposed. The calibration method was based on a polynomial error model, making the solution of each error term transformed into a problem solving the center of a circle trace, without reducing the solution precision. The method adopted a sliding load, a sliding short and a short circuit, thus reduced the requirements of standards in the millimeter-wave band. In experiment, a Ka-band reflectometer was built, the errors- solving processes and physical meanings were presented. After calibration, measurement results from reflectometer and vector network analyzer (VNA) were compared, and good agreement was achieved. Measurement results of a W-band corrugated horn were also compared, which further validate the method.