Is it possible that a same INSERT operation performance will suddenly degrade? I am working on a code performance test project. 

Let me first describe the enviorment: MsSql Server, Ria Service

The automation test runs a big set of Test cases in midnight where have minimum network traffic or CPU usage on the server.

The tests will calls the Ria Service and the Ria Service will make calls to the database to do same operation repeatedly for couples times.

The performance metric is measured using Sql Profiling Trace, so we got all sql calls that made within each test and we can associates each of them.

I notice sometime a same SQL calls in a test its performance will suddenly jump up.

i.e. An INSERT operation of a test, usually is around 0.807 ms and its jumps to 200ms.

I wonder is this a normal behavior?  Say there is no environment impacts to the test...
It could be blocked by another process, it could have forced an autogrow, something else may have taken the CPU's attention, data may have changed affecting cardinality, the plan could have been flushed, who knows? 

Basically, yes, the same query can behave differently at different times due to a variety of environmental factors, both inside SQL Server and external.