My wife had misscarriage 4 weeks baby. here temprature is near 40 celcius could this was the reason behind miss carriage.

It may be the other: Way around. Please take your wife to a doctor to see if she acquired an infection while her birth canal was open during the miscarriage.

It's possible: That fever caused pregnancy loss or pregnancy loss caused fever. Either way if the fever is present now, she needs to be checked right away. She will need to get antibiotics if she has a pelvic infection. That can threaten future fertility or even her life, so this is an emergency. Get to a hospital if not there already. There are circumstances where fever can cause miscarraige, but unlikely 4her.