An extendable light box of this invention, which can be collapsed as an enclosure-type light box or extended to a wide-open type of photography system, comprises a photography platform and left, right, back and top lamp-housing. The left, right and back lamp-housing are connected to the photography platform with a sliding/extending mechanism, such as a slide guide or shearing-type extending unit. The top lamp-housing stands on the back lamp-housing and connected with a rotating mechanism, such as a joint. The photography platform and the back lamp-housing can be combined into a unit. The photography platform can also be a lamp-housing, or/and with a rotating turntable embedded. At least one horizontal and vertical joint are configured on the sliding/extending mechanism for horizontal rotating and vertical folding. Therefore, those lamp-housings can be moved away from the photography platform or even rotate and fold to the height and direction for lighting.