Based on the test data of groundwater samples during two tidal cycles from monitoring well located at Donghaidao ahore, Leizhou Bay, the paper analyzed the variations of Ca2+, K+, Na+, Cl-, SO42-, TDS and total hardness. The results show that chemical elements' variation is apparent, ions is 35.65-3610.41mg/L with lowest K+ and highest Cl- and Na+ respectively. TDS is 4970.89-6441.48 mg/L and total hardness is 1054.75-1409.65mg/L, the statistical features of ions vary with tidal periods. The percentage of ions in chemical element is relatively stable and the groundwater type is Cl-·SO42-－Na+·Ca2+ featuring seawater intrusion, and the averaged concentration alignment of ions meet exponential allocation well in tidal cycles; Cl and Na have highest absolute amplitudes and SO42-and Na+ have highest relative amplitudes, both Na+ and Cl- take high proportion of ion strength I, ions re-pairing and salt effects are significant; γNa+/γCl- is 0.75-0.83, γHCO-3/γCl-is 0-0.015and SAR is 16.60,0.17in two tidal cycles in separation; linear correlations reveal that Cl- and Na+ have very good relationship with other elements,the averaged γCl-/γHCO-3shows high saline level and there are gentle increase of ions in tidal cycles with fitness slope k>0; groundwater quality is V type except hardness ranging is IV- V and the general assessment result is poor.