A　femtosecond　Ti:　sapphire　laser　is　focused　into　a　modulated　He-filled　slab　waveguide　to　generate　high-order　harmonics.　The　modulated　slab　waveguide　is　used　to　periodically　vary　the　intensity　of　the　laser　pulse　along　the　direction　of　propagation　in　order　to　implement　quasi-phase　matching　of　the　high-order　harmonics.　Experimental　results　show　that　compared　with　the　spectra　emitted　from　an　unmodulated　slab　waveguide,　there　is　an　obvious　increase　in　the　yield　of　high　harmonics　at　wavelengths　close　to　the　cutoff　region.　This　finding　is　in　agreement　with　theory　and　calculations　reported　in　previous　research.　Therefore,　our　experiment　indicates　that,　as　with　the　modulated　hollow-core　waveguide,　a　slab　waveguide　can　also　achieve　quasi-phase　matched　high-order　harmonics.