Previous studies have shown that frequent blood pressure fluctuations associated with respiratory events can lead to increased blood pressure levels at night and even during the daytime in patients with severe OSA with hypertension. Continuous monitoring of nocturnal blood pressure fluctuations in OSA patients, not all OSA patients exhibited significant apnea-related nocturnal BP surges, some patients' nocturnal blood pressure fluctuations were independent of respiratory events, some spontaneous contractions, without respiratory events, micro-arousal, and leg movement ,which can lead to transient increases in blood pressure. Moreover, some patients did not show significant BP fluctuation but with high baseline BP level. If hypothesis that nocturnal BP fluctuation was irrelevant to the respiratory events or no obvious BP fluctuations existence during sleep, in these case, even if apnea or hypopnea events were eliminated by CPAP treatment, but a low size in antihypertensive effect. If BP fluctuations were the closely related to respiratory events and frequent nocturnal BP fluctuations resulted in daytime and nocturnal hypertension, in these case, CPAP treatment can significant lower both daytime and nocturnal BP level. A number of previous studies have shown that the efficacy of CPAP in decreasing BP level was unsatisfied. The investigator supposes whether or not during the process of recruitment, the characteristics of blood pressure fluctuation of OSA patients were not considered and result in a false judgment that the inefficacy of CPAP treatment on lowering BP levels.