do you think it is reasonable to pick stocks at random by constroling the probability, such as pick one stock with probability 60%? or this is nonsense ?

Your question doesnt really make sense so I dont think anyone will be able to give you a good answer.

Thanks a lot. I do agree with you. But my boss ask me to consider such a problem. I feel falling into a deep depression.

Probability of what? You can't just talk about probability in a vacuum, it has to be about something. For example, probability of increasing tomorrow. Which brings into the discussion a bunch of assumptions that should be specified, because people here do not all agree on what the appropriate assumptions are.

Nope, I'm a student and do some research about how to pick stocks. Actually, I can show some detail about the model if you are interested in.