This paper will establish a general deformation equation group for two-hanging point horizontal boom of tower crane, therefrom its deformation and internal force can be universally calculated.

This article introduces the varieties of hoisting sling and the calcuation of secure work loads;the selection of common objects\'hoisting points and other things which we should pay our attention to while we are hoisting objects.

By using double hook screw crane and connecting two screw cranes by an intermediate bearing and a gear coupling,the problem of inefficiency in door closing was solved.