To meet the requirements of fiber laser applications under extreme temperatures or when there is a large temperature difference, it is necessary to develop fiber lasers able to operate in a wide temperature range. At present, there is a lack of reports on high-power fiber lasers that can operate in a wide temperature range with low power fluctuations. Thus, we designed a 1 kW fiber oscillator that can operate in a wide temperature range through temperature-related rate equations. The output characteristics of the oscillator are measured in the operating temperature range from -30∘C to 20°C. The experimental results show that the laser output power fluctuates by 7% over the entire temperature range. It was discovered that as the ambient temperature decreased, the efficiency of the laser decreased, and this issue is discussed in detail. This work has guiding significance for the design of high-power fiber lasers operating at a wide temperature range, and simultaneously, to the best of our knowledge, it provides the first kilowatt fiber oscillator that can operate in a wide temperature range between -30∘C and 20°C.