Why....why?

i was in thailand for 2 time, trying to open my own business there , but i found out ,that's i need a local partner.
so i don't understand ,why this law....

no one can take a partner like that... spasaly when u r new in the country

Yes its the law.  To open a business you must create a Thai company but you cannot own more than 49% of that company.  The other 51% must be Thai owned.