about reflect voltage

 With VOR= 210V your DRAIN voltage will be very very high. VDRAIN_SOURCE  would be the main concern with such high VOR.  Make sure your  DRAIN  voltage does not excedes the  MAX VD_S for the TOPSWITCH

the MAX VD_S for the top264 is 700v and with a max line of 280v ,,,,210+280*1.414=606V is less than 700v  ,i was confused because datasheet say that the MAX VOR is 135v but i think 210v is kind of ok.... 

When you have the power supply running at normal operation, Lets say 280VAC and full load, the TOPSwitch is switching On/OFF the current in the primary winding of the transformer (ILp). If you have an ideal transformer, (means magnetic coupling from primary to secondary = 1). Then all the flux in the core induced during the ON time of the controller will be transferred to the secondary circuit.

But since the world is not ideal, there is a flux in the core that links only the primary winding and it is not transferred to the secondary winding.  This leakage flux is like having an inductor in series with the primary winding of the transformer (Lk).  The voltage across Lk will follow the equation VLk= L(di/dt). So every time the controller is turned OFF during normal operation, Lk generates a voltage spike at the DRAIN node.  So this voltage spike due to Lk will flies very high and needs to be clamped with the clamping circuit you generally see at the DRAIN node of a typical  flyback circuit.  So as llong as you keep your VIN(*1.4) + VOR + VLk below 700V during all conditions, then you will be OK to design with larger VOR.

so when the circuit running at normal operation,the clamped circuit donot conduct(zener donot conduct),or it conduct everytime a spike is produce? I set the RCD clamps voltage to be 300v and i assume that when the primary switch turn off VOR+VIN*(1.4)=210+280*1.4=602V and due to the  spike voltage the RCD clamps will conduct and clamp the DRAIN voltage to VIN+VCLAMP=280*1.4+300=692V which is less than 700V.(that spike is plus on to 602v,but no matter how big that spike is the clamped circuit will always clamp the DRAIN at less than 700v,or in other words,VOR+VLK<=300 during all conditions)

It may be possible to design with such high reflected voltage.  But is not as simple as it looks to be. The clamp at the DRAIN node is subject to tolerances and variations due to temperature. For this reason I would recommend your measured peak voltage at the DRAIN to be no more than 660V. You need to measure the spike voltage at start up and when a load transient is happening and when the power supply is being overloaded. Need to be done at Maximum Vin and minimum Vin. You need to design a transformer with low leakage inductance. Split the primary in two primary windings in series and place the secondary inside the two primary windings. Place an RC network across the output rectifier. This will reduce the spike of the diode when it is switching. It is important to reduce this spike because it is reflected to the primary. Hope this advice will be helpful

i will rebuild my transformer

thanks for your help and advice!