The invention provides a working trough and a method for maintaining a uniform temperature of a working fluid. The working trough is applied to an electrical discharge machine that performs wire cutting using the working fluid. The method for maintaining a uniform temperature of the working fluid is applied to the working trough and characterized by forming opening structures in a receiving slot of the working trough such that a spiral swirl having a predetermined height is allowed to be formed in the working fluid, thereby maintaining a uniform temperature of the working fluid in the receiving slot when a wire cutting process is performed in the working fluid by the electrical discharge machine. The disturbance of the spiral swirl also facilitates the discharge of scraps. The present invention further has an advantage of low cost.