Abstract: When coupling with plasma the high intensity,long wavelength laser produces muchsuperthermal electrons,which lose their energy in following mechanisms:bremsstrahlung,collisionsand accelerating fast ions via electric field in corona.In some typical conditions the energy frac-tion lost for each mechanism has been analysed and estimated.The analytical expression ofbremsstrahlung spectra emitted in the slowing down of fast electrons passing through laserplasma has been given, With the parameters adjusted to fit the experimental results,the various in-formation for superthermal electrons,for example,their temperature,energy,number as wellas ener-gy spectrum,can be obtained.The computing spectra has compared with the experimentalspectra.