In this paper, breakdown voltage and on-resistance characteristics of the surface doped SOI RESURF LDMOSFET were investigated as a function of surface doping depth. In order to verify the variation of characteristics, two-dimensional device simulation was carried out. Breakdown voltage of the proposed structure is varied from $73 {~}138V$ while surface doping depth varied from $0.5{~}2.0{mu}m$. And on-resistance is decreased from $0.18{~}0.143{Omega}/cm^2$ while surface doping depth increased from $0.5 {~}2.0{mu}m$. Maximum breakdown voltage of the proposed structure is 138 V at $1.5{mu}m$ depth of surface doping, yielding $22.1\%$ of improvement of breakdown voltage in comparison with that of the conventional SOI RESURF LDMOSFET with same epi-layer concentration. On-resistance characteristic is also improved about $21.7\%$.