A new type of spectroscopic ellipsometer with polarizer and analyzer rotating synchronnously at a speed ratio of 1: 2, has been designed and constructed. An additional source polarizer was used to reduce the slight polarization effects of the light source.The light intensity includes one DC and four AC components, having the frequencies of ω0,2ω,3ω0 and 4ω0 respectively. Complex dielectric spectra can be obtained by claclating any three of the four AC signals, having data self consistency of better than 0.5%. The design, alignment and calibration of the system are discussed in detail. The results of measured spectra of Au and CdTe in the 1.5～4.5 eV range were presented and shown to be in agreement with the results of others.