Parallel FDTD method is used in time-domain simulation of large horizontally polarized electromagnetic pulse(EMP) bounded wave simulator with discrete resistors, in which the earth is set as lossy media truncated by uniaxial perfectly matched layer (UPML) absorbing boundary. Simulator's radiation fields in time-domain with different earth conductivity, earth relative dielectric constant and cone's radius are given. And electric field with a 10 m-length cylinder effector in simulator is also presented. The number of total cells in parallelized FDTD computing is about 1.8 billion. It shows that reflection from the earth becomes great as the earth's dielectric constant or conductivity increasing; The cone's radius has great effect on peak value of E-field in simulator, and fields at same horizontal plane becomes uneven as the radius becomes large; Reflection and loss from the earth have great effect on peak value and pulse width of E-fields in a horizontal plan above the ground 1 m, while they have little effect on E-fields in a horizontal plan above the ground 5 m. Energy entering into effector through a square hole is great as the hole is at the same side of simulator fields' leak.