Krzysztof Sontowski, 36, died after he was crushed by a reversing lorry at the site in February 2015.
Aylesbury Crown Court heard Mr Sontowski became trapped between the lorry and the loading bay.
DHL Supply Chain had admitted two breaches of the Health and Safety at Work Act last year.
Judge Francis Sheridan described Mr Sontowski’s death as a “dreadful and avoidable accident”.
The court was told Mr Sontowski, who was originally from Poland but lived in Milton Keynes, helped unload large goods lorries at the depot. On the day he died, he was at the rear of a vehicle and appeared to be trying to get the driver’s attention in the wing mirror.
The court was told he looked round and his head and torso became trapped between the lorry and the loading bay.
Judge Sheridan said Mr Sontowski’s death was as a result of a wheel-locking mechanism failing on equipment used to load and unload goods from lorries.
He referred to a similar failing in 2012 which was reported to managers but commented that they “failed to take the responsibility to deal with it.”
The judge said at that point “alarm bells really, really should have been raised.”
DHL was praised by Judge Sheridan for providing financial support to Mr Sontowski’s family after the accident. He said the company had taken the proceedings “exceptionally seriously” and failings reported after Mr Sontowski’s death had been addressed.
A spokeswoman for DHL said: “We accept the judge’s findings and the fine handed down.
“Once again we offer our sincere condolences to Mr Sontowski’s family and repeat that the safety of our colleagues and the public remains paramount to the company.”
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