This paper is considered with the finite time stability (FTS) for positive nonlinear systems. First, the fuzzy copositive Lyapunov function (FCLF) is established to reduce the conservatism of FTS conditions. Then, by using FCLF, a new FTS criteria of the studied systems is established. Since, the time-derivatives (TD) of membership functions are considered in the stability analysis, our results are less conservative. Besides, the obtained conditions are expressed via the linear programming technique, that can be verified effectively. Finally, the pest-predator system is used to reflect the effectiveness of the results.