Based on wave measurements lasting three and a half years, typhoon wave characteristics in a lagoon of the South China Sea are discussed in this paper. According to the upper boundaries of wind speed and significant wave height H_s, the maximum wave height has a similar rate of change as the maximum wind speed. The peak frequencies decrease in the approaching stage and are concentrated with an average of 0.1415 Hz in the leaving stage. The distributions of the wind and wave directions indicate that the local wind waves and the waves from the open sea propagated to the site in the approaching and leaving stages, respectively. Wind waves generated inside the lagoon are fetch-trapped, and the spectra can be described by αf⁽⁻⁴⁾ or βk^(−2.5) when f > f_p. In addition, the measurements show that the nondimensional maximum spectrum can be estimated by the nondimensional fetch. The spectra of the waves from the open sea can be described by . Parameters a and c are determined by the nondimensional peak frequency. In addition, it is found that the peak energy density S(f_p) is a linear function of for all waves.