This paper reports on the combustion characteristics of mixed fuel droplet of fluid catalytic cracked (F. C. C.) bottom based fuel and Diesel Oil by an improved equivalent-comparison method. The combustion characteristics under different degrees of Diesel Oil content of F.C.C.B.B. fuel are investigated. In the experiment, the effect of Diesel Oil content affects, the latent heat, ignition delay, the mean combustion rate, and the combustion efficiency of the mixed F.C.C.B.B. fuel are addressed. As the Diesel Oil content in the F.C.C.B.B. fuel increases, the mean combustion rate, and combustion efficiency increase, while the ignition delay decreases. The burning time is shorter, the amount of residue is less, and the degree of smoking is lighter for mixed F.C.C.B.B. fuel than that of un-mixed F.C.C.B.B. fuel.