A wave power converting device, comprising: a platform, the platform having a retaining post anchored to an underwater ground; a plurality of first fluid guide assemblies assembled to the platform, each of the first fluid guide assemblies having a first guide tube and a first side tube, the first guide tube disposed underwater with one end, the first side tube extended upwardly from one lateral side of the first guide tube; a plurality of second fluid guide assemblies assembled to the platform, each of the second fluid guide assemblies having a second guide tube and a second side tube, the second guide tube disposed underwater with one end, the second side tube extended downwardly from one lateral side of the second guide tube; and a floating assembly, the floating assembly having a top plate, a bottom plate and a connecting rod, the floating assembly assembled to the platform and the floating assembly being movable up and down relative to the platform, the top plate having a plurality of first pistons extended downwardly therefrom, each of the fist pistons inserted into the respective first side tube, the bottom plate having a plurality of second pistons extended upwardly therefrom, each of the second pistons inserted into the respective second side tube, the top plate having a plurality of positioning grooves defined around an outer periphery thereof, the adjacent positioning grooves being separated by a distance, the first fluid guide assemblies and the second fluid guide assemblies being located in the corresponding positioning grooves; wherein, when the buoy body is moved by the waves so as to drive the floating assembly moved up and down, the water flows into the first guide tube and the second guide tube and the water in the first guide tube and the second guide tube is pressed upwardly via the reciprocation of the first piston and the second piston, so that the water flows upwardly to a reservoir above the platform. a platform, the platform having a retaining post anchored to an underwater ground; a plurality of first fluid guide assemblies assembled to the platform, each of the first fluid guide assemblies having a first guide tube and a first side tube, the first guide tube disposed underwater with one end, the first side tube extended upwardly from one lateral side of the first guide tube; a plurality of second fluid guide assemblies assembled to the platform, each of the second fluid guide assemblies having a second guide tube and a second side tube, the second guide tube disposed underwater with one end, the second side tube extended downwardly from one lateral side of the second guide tube; and a floating assembly, the floating assembly having a top plate, a bottom plate and a connecting rod, the floating assembly assembled to the platform and the floating assembly being movable up and down relative to the platform, the top plate having a plurality of first pistons extended downwardly therefrom, each of the fist pistons inserted into the respective first side tube, the bottom plate having a plurality of second pistons extended upwardly therefrom, each of the second pistons inserted into the respective second side tube, the top plate having a plurality of positioning grooves defined around an outer periphery thereof, the adjacent positioning grooves being separated by a distance, the first fluid guide assemblies and the second fluid guide assemblies being located in the corresponding positioning grooves; wherein, when the buoy body is moved by the waves so as to drive the floating assembly moved up and down, the water flows into the first guide tube and the second guide tube and the water in the first guide tube and the second guide tube is pressed upwardly via the reciprocation of the first piston and the second piston, so that the water flows upwardly to a reservoir above the platform.