Leaf　area　index　(LAI)　is　an　important　parameter　of　canopy　structure,　Decause　it　relates　to　many　biophysical　and　physiological　processes　of　canopy,　including　photosynthesis,　respiration,　transpiration,　carbon　cycling,　precipitation　interception,　and　energy　exchange,　etc.　This　paper　introduced　the　theoretical　bases　and　mathematical　models　of　optical　methods　for　forest　canopy　LAI　determination,　introduced　the　principles,　merits,　and　drawbacks　of　currently　used　optical　methods,　and　summed　up　the　main　sources　of　the　errors　in　LAI　optical　measurement,　including　clumping　effect,　non-photosynthesis　components,　measurement　conditions,　and　terrain　effect.　The　developing　status　of　quantitatively　evaluating　clumping　effect,　non-photosynthesis　components,　and　terrain　effect　was　analyzed,　and　the　promising　development　directions　of　optical　methods　for　measuring　forest　canopy　LAI　were　discussed.