High Jc MgB2 superconducting bulks doped with carbon nano-tubes (CNTs) were prepared by a diffusion method, and their superconductivity was compared with that of CNTs-doped MgB2 prepared by a conventional solid-state reaction method. Results show that the novel diffusion method can increase the density of MgB2 bulks remarkably and reduce the adverse effect of oxygen in Mg powder. The MgB2 bulks prepared by the diffusion method are more uniform with less MgO impurity, so that they have higher critical current density in the self field. But the properties are improved a little in high field; however, MgB2 can overcome the shortcomings in high-field notably by CNTs doping. For the MgB2- sample with 0.5% CNTs doping under the condition of 10 K and 4 T, Jc is as high as 1.0×104 A/cm2 and it reaches 0.46 MA/cm2 in zero field, which is 2 to 3 times higher than that of the MgB2 samples by the solid-state reaction under the same condition.