Abstract: The theory of the heating of the solar wind by the Alfvenic fluctuation and two models for the attenuation of the Alfvenic fluctuation (Viscous model and Wave energy cascading model) have been tested against the observed data by Helios 1 and 2. The calculation showed that, in the space range where Helios observed, (1) from the energy equation under the assumption that the Alfvenic fluctuations changes into the heat energy of the solar wind protons, the calculated radial variation of the temperature of the solar wind protons agrees with the observed results; (2) the rate of the energy dissipation of the fluctuations predicted by the viscous model is different from the observed results. The difference is about 8 orders, so it can not discribe the process of the energy dissipation; (3) the rate of energy dissipation of the fluctuations predicted by the wave energy cascading model agrees with the observed results. The possible mechanism of the heating of the solar wind protons is the dissipation of the energy cascading to the frequency range of the proton gyro-frequency.