Resource size, group size, cost and other's strategy were manipulated in four experiments using a forest manager simulation game, in which players planted seedlings and harvested trees as they grew. The game was repeated so that there were more than 20 trials. Results indicated that the less resources there were, the less cooperation there was, but the cooperative aspect of players' behavior could be improved by introducing costs and/or stooges, employing some certain strategies. And the most intensive cooperation was obtained under two tree-two person condition, enabling for the“one for one person”quota effect to take place. Subjects reported their motives, strategies and estimations of ranking of the levels of cooperation among various resource sizes in their responses to questionnaire and in face-to-face discussions. The discrepancies between the cognition of subjects and the observed behaviors were discussed.