Diesel reforming was investigated as a method to supply fuel for SOFC(Solid Oxide Fuel Cell). Objective of this paper is to draw actual problems which happen when a diesel reformer combines with a SOFC stack. ATR(Autothermal Reforming) was used to reform diesel. S/C(Steam to Carbon ratio), O/C(Oxygen to Carbon ratio), GHSV(Gas Hourly Space Velocity) and temperature of reactor were manipulated to control operating conditions of diesel reformer. Those conditions directly affected the performance of a SOFC stack. Other detailed conditions of the reactor also caused power change of SOFC.