Nowadays, the studies on band gap and absorption spectrum of TiO2 doped with Pr lead to opposite conclusions. Two experimental results about red-shift and blue-shift are reported in the literature. We have set up models for pure TiO2 and different doping concentrations of Pr-doped TiO2 to calculate the electronic structure and absorption spectrum based on the first-principle plane-wave ultrasoft pseudopotential in terms of the density functional theory (DFT) to slove the above problem. Results indicate that under the condition of heavy doping Pr, compared with the pure TiO2, as the Pr concentration increases the atomic charge of the doped system reduces and the total energy of the doped system becomes higher, and its formation energy will be greater. This makes the stability decline, the band gap narrowed, the absorption spectrum red-shift, and the absorption strength more significant. The results of the calculation is in agreement with the experimental data.