Abstract: A novel multi-arm polyethylene glycol (PEG) (I) and preparation method thereof. Active derivatives (II) based on the multi-arm PEG. Gels formed of the active derivatives. Drug conjugates formed of the active derivatives and drug molecules and uses thereof in medical preparation. The multi-arm PEG is formed by polymerizing ethylene oxide with pentaerythritol oligomers as initiator, wherein PEG is the same or different and is a —(CH2CH2O)m-, the average value of m is an integer of 3-1000, l is an integer more than or equal to 2. An 8-arm PEG is preferred, wherein l is equal to 3. The active derivatives (II) comprise link groups X attached to PEG and active end groups F attached to X.