A Ka-band antipodal finline waveguide-to-microstrip transition was analyzed and simulated by HFSS software. The several factors of simulation result for affecting performance of transition are analyzed, and a design curve of transition available for project application is obtained. Based on the curve, the waveguide-to-microstrip transition is designed. The insertion loss of transition is below 1 dB in the Ka-band. Experimental results coincide well with the design curve.