Diversification strategy is a common and important method for enterprises to expand business scope, effectively use resources, and improve economic benefits. However, not all companies that have adopted a diversified strategy will be successful. There are still some controversies about the relationship between diversification strategy and firm performance. Based on summarizing the diversification theory, this paper evaluates the performance of Gree Group under the diversification strategy through financial indicators, Tobin's Q value, and share of revenue. We draw a conclusion that Gree's current diversification strategy is not suitable for the future development of the enterprise and provide suggestions about the adjustment of Grees diversification strategy.