my effect 901 (circle) run as a "8" figure

this is expected behavior.

effect 901 doesn't make your fixture draw a circle no matter what, it sends pan/tilt values.

so in the marked section (going counter-clockwise) this graph says that the pan value decreases while the tilt value increases. the difference of pan in the beginning of this quarter and the end of this quarter is the amount in Scale (by default 25). tilt increases by the same amount.

so if you apply the effect to a moving light that is currently at pan/tilt 0°/0°:
3 o'clock = 25°/0°
12 o'clock = 0°/25°
9 o'clock = -25°/0°
6 o'clock = 0°/-25°

but you were expecting:
3 o'clock = 0°/25°
12 o'clock = 90°/25°
9 o'clock = 180°/25°
6 o'clock = 270°/25°
you can see that in this effect tilt doesn't change. only 1 parameter changes, so you're actually looking for a linear effect.

and just as a side note: 95% of all moving lights can't do this movement because they don't have infinite pan. usually you can do 1.5 turns (that's 540°).

this whole math changes (or actually the math is still the same but the results are different) as soon as you try to do a circle where 0°/0° is outside of the shape. so e.g. if you tilt a moving light to tilt 90°, effect 901 will give you an actual circle.

so how can i make the circle effect 

around the home position you can't make a circle effect because of physical limitations of the fixture.

around the home position you can't make a circle effect because of physical limitations of the fixture.