Based on the digital observatory data of pendulum tilt-meter and water tube tilt-meter, spheroidal modes of earth’s free oscillations, induced by the MS8.0 Wenchuan strong earthquake occurred on May 12, 2008, was obtained with the method of power spectral density estimation without any calculation to erase solid tide. The result matches well with the PREM’s when it is compared with the theoretical free oscillation of PREM model with the exception of _0S7, and the relative errors that are mostly bigger than 0.3%. All other relative errors concentrate on 0.1%. This research provides a new method to get spheroidal modes of earth’s free oscillations from observatory data of pendulum tilt-meter and water tube tilt-meter, which may be useful in the future of the earth’s free oscillations research.