The　Lempel-Ziv　algorithm　is　not　fully　suitable　for　measuring　the　complexity　of　short　series.　When　the　Lempel-Ziv　algorithm　is　applied,　the　assumption　that　the　sequence　must　he　long　enough　is　always　ignored:　the　series　length　is　usually　too　large,　and　the　equi-probability　assumption　also　is　not　considered　in　some　papers.　Based　on　these　facts,　the　universal　algorithm　of　trial　and　error　is　presented　when　the　conditions　of　different　sequence　lengths　and　different　symbol　probabilities　are　comprehensively　considered　The　facts　that　the　over-valuation　would　occur　in　measuring　normalized　complexity　of　short　sequences　with　the　original　Lempel-Ziv　algorithm　and　obtained　results　through　improved　Lempel-Ziv　algorithm　more　in　accord　with　the　reality　are　testified　by　virtue　of　tests　of　ultra-short　series,　Logistic　equation　of　different　state,　observed　traffic　flow.