In the last decade,the femtosecond pulse filamentation in transparent media has been extensively studied by many research groups[1] and made great achievements in many practical applications such as water vapor concentration measurement,[2] laser-filamentation-induced snow formation,[3] plasma grating generation,[4] and third harmonic enhancement.[5-7] The underlying mechanism of femtosecond pulse filamentation has been widely accepted as the dynamic interaction between the optical Kerr effect due to nonlinear intensitydependent refractive index and plasma defocusing originated from multiphoton/tunnel ionization.The laser intensity inside the filament is clamped to ～5 × 1013 W/cm2 in air.This intensity is high enough to dissociate/ionize air molecules and excite the ions or molecules into some highly excited states,resulting in the emission of characteristic fluorescence.[8]All the physical mechanisms and applications of the laser plasma filament involve the most basic characteristic research of filaments.Therefore,it is important to precisely characterize the plasma temperature,density and spatiotemporal evolution.