In this paper the authors analyze the factors which influence the economy of trawlers for a system comprising trawlers, fishing ground, fishing market and fishing port. The important influential factors are fish price Fp, richness degree of fishing ground K and oil price Op. There is a range of optimum speed for certain objective conditions. The optimum speed of trawlers can be decided according to K and Fp/Op. The steps and method to find out the optimum speed of trawler under the influence of uncertainties are described.