The present invention provides a novel multi-arm polyethylene glycol (I) formed by ethylene oxide polymerization with oligomeric pentaerythritol as an initiator and its use, in which the PEGs are the same or different -(CH 2 CH 2 O) m - the average of m is an integer of 3-1000 l is an integer ‰¥2 and especially provides an eight-arm PEG with l equal to 3. The present invention also provides a method for preparing the multi-arm PEG as described, active derivatives of the multi-arm polyethylene glycol (–¡) connected to the linking group X of PEG and the active end-group F of X, gel formed from the active derivatives of multi-arm polyethylene glycolas described, pharmaceutical conjugates formed from the active derivatives of multi-arm PEG as described and pharmaceutical molecules as well as their uses in manufacturing medications.
