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Intensive studies have been conducted to understand the anisotropy of solarwind turbulence. However, the anisotropy of Els\"asser variables($\textbf{Z}^\pm$) in 2D wave-vector space has yet to be investigated. Here wefirst verify the transformation based on the projection-slice theorem betweenthe power spectral density PSD$_{2D}(k_\parallel,k_\perp )$ and the spatialcorrelation function CF$_{2D} (r_\parallel,r_\perp )$. Based on the applicationof the transformation to the magnetic field and the particle measurements fromthe WIND spacecraft, we investigate the spectral anisotropy of Els\"asservariables ($\textbf{Z}^\pm$), and the distribution of residual energy E$_{R}$,Alfv\'en ratio R$_{A}$ and Els\"asser ratio R$_{E}$ in the$(k_\parallel,k_\perp)$ space. The spectra PSD$_{2D}(k_\parallel,k_\perp )$ of$\textbf{B}$, $\textbf{V}$, and $\textbf{Z}_{major}$ (the larger of$\textbf{Z}^\pm$) show a similar pattern that PSD$_{2D}(k_\parallel,k_\perp )$is mainly distributed along a ridge inclined toward the $k_\perp$ axis. This isprobably the signature of the oblique Alfv\'enic fluctuations propagatingoutwardly. Unlike those of $\textbf{B}$, $\textbf{V}$, and$\textbf{Z}_{major}$, the spectrum PSD$_{2D}(k_\parallel,k_\perp )$ of$\textbf{Z}_{minor}$ is distributed mainly along the $k_\perp$ axis. Close tothe $k_\perp$ axis, $\left| {E}_{R}\right|$ becomes larger while R$_{A}$becomes smaller, suggesting that the dominance of magnetic energy over kineticenergy becomes more significant at small $k_\parallel$. R$_{E}$ is larger atsmall $k_\parallel$, implying that PSD$_{2D}(k_\parallel,k_\perp )$ of$\textbf{Z}_{minor}$ is more concentrated along the $k_\perp$ direction ascompared to that of $\textbf{Z}_{major}$. The residual energy condensate atsmall $k_\parallel$ is consistent with simulation results in which E$_{R}$ isspontaneously generated by Alfv\'en wave interaction.

Spectral Anisotropy of Els\"asser Variables in Two Dimensional Wave-vector Space as Observed in the Fast Solar Wind Turbulence