How to calculate whether the pump I'm using is suitable for my system? I want to fill a water tank from a river to the tank up hill. The head from the pump to the tank is approx. 50meter. The distance and pipe I'm going to lay is approx. 100meter from pump to the tank. Which mean approx. 45deg diagnal. I'm using a 1inch size poly pipe to bring the water from pump to the tank. Is it OK to use a 6.5hp pump? Any help in calculation?

Maybe in your excitement you forgot something
What is the GPH and the LIFT rating on your pump there's your answer.
You ask if the pump you are using will do the job. If you can't provide pump info as said above then it's a wash. The best if the best engineers could never answer your question with out pump ratings.

Happy New Year!