MPU6050_DMP6 output is not stable

[xuxubin]

Hi,
I am using the MPU6050_DMP6.ino for the Arduino UNO. I get the QUATERNION data like this:

-0.31,-1.95,0.62,0.42,
-0.00,0.48,-0.00,0.16,
-1.96,-0.86,0.22,-0.07,
0.42,-0.36,0.56,0.00,
0.16,-1.21,-1.37,1.21,
1.33,0.27,1.25,-0.98,
0.00,0.00,-0.00,0.48,
-0.94,-1.96,0.02,-0.14,
-1.63,0.62,0.42,-0.36,
0.48,-0.00,0.16,-1.21,
1.95,0.56,0.97,-1.70,

the data is not stable even the MPU_6050 is static.
Also the data is strange.
the code is like this:

#ifdef OUTPUT_READABLE_QUATERNION
// display quaternion values in easy matrix form: w x y z
mpu.dmpGetQuaternion(&q, fifoBuffer);
 //Serial.print("quat\t");
Serial.print(q.w);
Serial.print(",");
Serial.print(q.x);
Serial.print(",");
Serial.print(q.y);
Serial.print(",");
Serial.print(q.z);
Serial.println(",");
#endif

What are the possible reasons?
I am sure that the wiring between the UNO and MPU6050 is correct.
Thank you!