I know the annual average wind speed in my site. To calculate energy from a wind turbine i have to know the weibull parameter K.Is there any way to calculate this from only annual average wind speed. Please inform me.

The average wind speed and the Weibull k parameter are two independent variables.  There is no way to determine one from the other.  Whenever I have no information about the Weibull k, I always use a value of 2.  Using that value in a model like HOMER will give you a rough guess as to the output of a wind turbine at your site.  For a better estimate of the Weibull k, you could look for measured wind data at a nearby site, or you could look for something like a wind atlas for Bangladesh.  Note that the SWERA project covers Bangladesh, and they might provide relevant data.