Levitated nano mechanical resonator is a newly developed detection method of high-precision measurement. Thanks to the high Q factor, it is promising in a wide range of fields including weak force detection, wave function collapse measurement, and so on. The mechanism of feedback cooling is discussed in this paper. In addition, NdFeB permanent magnets are used to perform diamagnetic levitation of polyethylene glycol 600. In an experiment in this paper, a micro coil is used for feedback cooling for two modes to reach hundreds of Kelvin under 300 K and 10-5 mbar vacuum condition. The experiment result agrees with the theoretical lowest effective temperature, which paves way for a further research on macro quantum phenomena.