Terahertz (THz) extremely large-scale massive MIMO (XL-MIMO) has emerged as a potential key enabling technology for 6G due to its advantages such as wide bandwidth and high beam gain. However, before the design and deployment of the THz XL-MIMO system, it is crucial to understand its channel characteristics. In this paper, we first perform THz XL-MIMO channel measurement, revealing substantial variations in multipath power across antenna elements. Subsequently, an analysis of the large-scale parameters of the THz XL-MIMO channels is conducted. The results indicate significant fluctuations in delay spread, angular spread, and multipath component (MPC) power distribution across the XL-MIMO antenna elements, with maximum differences of 9.49 ns, 45.42°, and 16.29 dB, respectively. Finally, the near-field, spatial nonstationarity (SnS), and beam misalignment characteristics of THz XL-MIMO are discussed from both line-of-sight (LoS) and reflection paths, highlighting that the SnS parameter follows a Gamma distribution. This paper aims to provide valuable insights into the systematic design and optimization of THz XL-MIMO by delving into its channel characteristics.