The invention provides a series-connection type transformer cooler. A box body is in a rectangular shape, hollow heat exchange pipes penetrate through baffles at the upper end and the lower end of the box body and fixed to the baffles, an upper end cover is fixedly connected to the upper baffle of the box body, a closed space is formed between the upper cover plate and the box body, a lower end cover is fixedly connected to the lower baffle of the box body, a closed space is formed between the lower end cover and the box body, a front end cover and a rear end cover are arranged on the two sides of the box body, the front end cover is provided with an air outlet, and the rear end cover is provided with an air inlet. A front cover plate is connected with the box body through a box body flange, the rear end cover is connected with the box body through a box body flange, fans are arranged in air pipes on the front cover plate, and the upper end cover and the lower end cover are of a waveform structure. When the number of the lines of the heat exchange pipes is an odd number, a water outlet pipe is arranged on the left side of the lower end cover, and a water outlet pipe is arranged on the right side of the upper end cover. When the number of the lines of the heat exchange pipes is an even number, a water inlet pipe is arranged on the left side of the lower end cover, a water outlet pipe is arranged on the right side of the lower end cover, and neither the water inlet pipe nor the water outlet pipe is arranged on the upper end cover. According to the series-connection type transformer cooler, the overall heat exchange effect of the cooler can be improved.