An intensive research have been done about the W-band sheet beam klystron (WSBK) for its potential value in active denial system application. The output cavity has an important influence on the output power, efficiency, bandwidth and spectrum. In this paper, multiple types of quasi-optical (QO) output couplers are designed based on the theory of equivalent dipoles and phase superimposition, and detailed study on the cold characteristics such as R/Q, M, loaded Q and mode uniformity has been all demonstrated. Compared with other tapers, QO output coupler with parabolic taper shows more excellent performance than the linear, triangle and Chebyshev tapers. We will receive benefit from improving the beam-wave efficiency and bandwidth of WSBK. Besides, a QO-output coupler with linear taper for initial experiment is fabricated.