If I want to calculate the movements of each moving objects driven by regular algorithm, then how can I measure required computing power? Is required computing power proportional to the quantity of the objects?
Have a look at Big-O Notation.
The core of an answer is already part of your question:
"... the movements of each moving objects driven by regular algorithm ...". So, if you have N objects, then the computation power needed is N times the computation power needed by the "algorithm".
Does the algorithm depend on other objects? Maybe because of collision detection or so? Then the computation power needed will typically increase more than linear with N.
If you don't have the years of experience so you can estimate the required computation power in advance, then implement your program and measure its performance.