呢兩句意思係咪都係大同小異？

Both sentences are correct in grammar.

My understanding of their meanings:

1. The man is wearing the same sweater as you.

~ The man is wearing a sweater exactly like the one you are wearing.
(= Both the man and you are wearing the same sweater.)

2. The man is wearing the same sweater as yours.

~ The man is wearing a sweater that is of the same type as your sweater.

The second one as yours - is better English

lst one is not correct but people understand what you mean

Thanks EICA.

From The Free Dictionary:
You can put a noun between the same and as. You can say, for example, 'She goes to the same school as her sister'.
Her dress was the same colour as her eyes.
I'm in the same type of job as you.

2015-05-06 20:53:54 補充：
You can also use the same as to compare actions. For example, you can say 'She did the same as her sister did', or just 'She did the same as her sister'.

2015-05-06 21:04:07 補充：
The two sentences are both correct but the meaning slightly different.:
The man is wearing the same sweater as you.- comparing actions
The man is wearing the same sweater as yours.- comparing things

2015-05-06 21:16:18 補充：
The man is wearing the same sweater as you.- comparing action那男子正和你穿着相同的毛線衣。
The man is wearing the same sweater as yours.- comparing things那男子正穿着和你相同的毛線衣。

第一句指你就是那件SWEATER。