that should be because of

lazy PID values or accelerometer
or
gyro orientation missmatch
or
vibration to the sensors (wire arrangements in your quad should amplify the vibrations they should be tied down or length shorten also try increasing/decreasing accelerometer filter in multiwii.)

Ohk
Wht are the minimum PID values for a 500*500 quad
With 1000 Kv motots and 1045 props
As for now mines are all set to zero

Have a look at this site very well explained!
http://blog.oscarliang.net/quadcopter-pid-explained-tuning/

default PIDs work near good, but that not zero(sometimes need to click "Read" button below that window to show values).

try
Pitch and Roll
P: 3.3 I: 0.030 D: 23

Yaw
P: 6.8 I: 0.045 D: 0

Ohh thanks a lot
And remaining all values are also set to zero