I can't set initial value of date time field

i try every way to set the initial value of date time field but i can’t. Please give me some advice.

starting point: how are you setting it?

first :
i set it by Control => Fields => date field => General Settings => Initial values (set by Define Values and System Date already but it’s still not working)
second :
set by Onload event (control app)

how should i do??

sorry for my expression and grammar. i’m not good in English.
thank you

It should work at the onload event, but I expect your problem is in the date-time format. The display format is not the internal format.