A tidal current energy generating device, comprising: an outer frame (1; 1'); at least two inner frames, separably disposed in the outer frame; at least two mounting shafts, rotatably disposed in the two inner frames, respectively, an axial direction of the at least two mounting shafts being perpendicular to a horizontal plane; a driving unit, connected with the at least two mounting shafts to drive the mounting shafts to rotate. at least four horizontal-axis hydraulic generators, every two horizontal-axis hydraulic generators fixed at one mounting shaft and disposed in the same inner frame, and the at least four horizontal-axis hydraulic generators changing directions with the rotating of the driving unit; and at least six bearings (5; 5'), every three bearings (5; 5') sleeved on one mounting shaft, and the three bearings (5; 5') on one mounting shaft disposed on the two sides of the two horizontal-axis hydraulic generators and between the two horizontal-axis hydraulic generators, respectively; and characterized by an underwater shaft rotating protecting device, wherein the underwater shaft rotating protecting device (7; 7') comprises: a lubricant storage tank, wherein a lubricant is stored and the lubricant storage tank is disposed above water surface, and the lubricant is sea water without impurities; at least six seal rings (72; 72'), every two seal rings (72; 72') corresponding to one bearing (5; 5') and sleeved on the mounting shaft, and a lubricant cavity (75; 75') being formed between every two seal rings (72; 72') and the corresponding bearing and the mounting shaft; and a tube, one end of the tube is communicated with the lubricant storage tank, and the other end communicated with the lubricant cavity (75; 75'). an outer frame (1; 1'); at least two inner frames, separably disposed in the outer frame; at least two mounting shafts, rotatably disposed in the two inner frames, respectively, an axial direction of the at least two mounting shafts being perpendicular to a horizontal plane; a driving unit, connected with the at least two mounting shafts to drive the mounting shafts to rotate. at least four horizontal-axis hydraulic generators, every two horizontal-axis hydraulic generators fixed at one mounting shaft and disposed in the same inner frame, and the at least four horizontal-axis hydraulic generators changing directions with the rotating of the driving unit; and at least six bearings (5; 5'), every three bearings (5; 5') sleeved on one mounting shaft, and the three bearings (5; 5') on one mounting shaft disposed on the two sides of the two horizontal-axis hydraulic generators and between the two horizontal-axis hydraulic generators, respectively; and characterized by an underwater shaft rotating protecting device, wherein the underwater shaft rotating protecting device (7; 7') comprises: a lubricant storage tank, wherein a lubricant is stored and the lubricant storage tank is disposed above water surface, and the lubricant is sea water without impurities; at least six seal rings (72; 72'), every two seal rings (72; 72') corresponding to one bearing (5; 5') and sleeved on the mounting shaft, and a lubricant cavity (75; 75') being formed between every two seal rings (72; 72') and the corresponding bearing and the mounting shaft; and a tube, one end of the tube is communicated with the lubricant storage tank, and the other end communicated with the lubricant cavity (75; 75'). a lubricant storage tank, wherein a lubricant is stored and the lubricant storage tank is disposed above water surface, and the lubricant is sea water without impurities; at least six seal rings (72; 72'), every two seal rings (72; 72') corresponding to one bearing (5; 5') and sleeved on the mounting shaft, and a lubricant cavity (75; 75') being formed between every two seal rings (72; 72') and the corresponding bearing and the mounting shaft; and a tube, one end of the tube is communicated with the lubricant storage tank, and the other end communicated with the lubricant cavity (75; 75').