3ω method has been investigated and its applications are analyzed. A wide appli cations in measuring the thermal conducti-vity and specific heat of material s are discussed. Here we discuss the mechanism of this method and introduce some basic applications. With some calculations in the two dimensional tunnel juncti on arrays and applications of 3ω method, a fast, primary Coulomb blockade therm ometer can be realized with a super-high precision in measuring temperatures in the Coulomb blockade regime.