Abstract: the　measuring　princi ple 　of 　hydrostatic 　levelin g　system　and　the 　tidal 　effects 　on　measurementaccurac y　of　hls　is 　introduced 　in 　this　paperand　harmonic　anal ysis 　of 　the 　tilt 　tidal 　observations　basedon　hls　is 　completed．hi gh－accurac y　tilt 　tidal 　model　and　parameters 　are 　obtained　afterwards．and 　thetidal 　correction　of 　the　hls　data　based　on　local 　tidal 　model　is 　completed thus 　the 　actual 　ground　de－formation 　is 　obtainedthe 　current 　research 　establish　a　foundation 　for　hls　application 　in　hi gh　accurac yali gnment　of 　particle 　accelerator