Hi guys i use the core i7 920 almost one month already all the things looking so good but one day i check the Temperature of my cpu using the core temp 0.99 it found out the Temperature of my cpu is
idle 55°C
load 95°C

The Temperature is so high but it not effect my pc at all no hang, lag or keep rebooting?

I did not overclock my pc !!!
My room is open the A.C and temp is around 18°C
All the things in my cpu are all new and i double check my thing it look fine. Why this will be happen? Can tell me reason please

My PC spec are:
Intel Core i7 920 D0
Asus Rampage II Extreme
CM Hyper N520 heatsink
CM PSU Real Power 550W
Asus GTX250 1G Dark Knight
Kingston DDR3 2G
SEAGATE 1TB Hard disk
Lite-on DVD Writer
Creative Sound Blaster Xi-Fi
CM HAF 922 Casing

It may be worth removing the CPU's heatsink and fan, giving them a good dust out, then putting some fresh thermal paste on there as it can dry out.

That's a REALLY hot temperature. I got a i7 920 build also and it used to run at about 60C idle and 70~75C load. Then I got a new heat sink/fans and tried out a new thermal paste called ARCTIC COOLING MX-2 instead of Artic Silver 5.

Any who after the change my rig ran at about 45C idle and 670C max load. My room environment temperature is natural temperature from outside(2 windows open) so it varies from 75~85F whatever the weather is so that's not affecting the cooling at all.

Okay that's enough comparisons now what I think is that you would either have a airflow problem and that there isn't enough cool air flowing into your case, but I don't think that's the problem at all. If anything it would be that you would want to reapply some thermal paste because it seems you did not put enough or its dried out, like Rik said.

What I actually did when I applied the MX-2 is something that I was always told not to do when applying thermal paste and what I got was 20C drop in temp so I'm going to use this for now on.

1. clean surface of heat sink copper and cpu where thermal paste will be with rubbing alcohol or the arctic silver purifying kit if you have some.
2. Apply thermal paste lightly on BOTH the cpu and heatsink(this is something that I never did before) and if your heatsink has textures on it from the smoothing it went through remember to get a nice even coat on it to fill in any possible air pocket that might form.
3. when you place on the heat sink on the cpu make sure you place it firmly and don't lift it at all and twist it slightly counter clockwise and clockwise gently.

Well that's all I would honestly say because its the first time I actually applied thermal paste in that manner. As for my specs to use as refernce here they are and a Screen

CPU: Intel Core i7 920 D0 2.67GHz OC->3.35GHz
Heatsink/Fans:Thermalright ULTRA-120 Extreme Black Edition (2x Nocta NF-P12 in Push-Pull)
Case Fans: 6x Scythe S-FLEX 120mm
PSU: Thermaltake Toughpower W0133RU 1200W
GPU: BFG Tech GeForce GTX 295
Hard Drives: 2x Seagate 1TB; 4x Seagate 1.5TB

Idle SS
Load SS