The spectral responsibility of 6H-SiC pn junction ultraviolet photode tector has been simulated by 2D numerical model. The effect of different impurity concentration and different junction-depth on the responsibility is discussed in this paper. For p+n device, the responsibility can be as high as 167.2 mA/ W when the width of p+ layer is about 0.2μm, and the impurity concentrations are about 9×10.18cm-3and 1×10.6 cm-3 in p+layer and nlayer, re spectively. For n+p device, the responsibility is as high as 183.5 mA/W when the width of n+-layer is about 0.2μm, and the impurity concentrations are abo ut 9× 10.18cm-3 and 1×10.6cm-3in n+-layer and p-layer, respe ctively. It is shown that the result of simulation agrees with the experimental data very well.