The invention provides a settling algae collection device which comprises a cylindrical guide column. A filter screen is arranged at an inlet in the top of the guide column, a screen fixing cover for fixing the filter screen to the top of the guide column is arranged on the filter screen and is provided with an inlet, the bottom of the guide column is connected with a collection disc, the bottom of the side wall of the guide column is provided with a water outlet pipe, and the bottom of the collection plate is provided with a discharge pipe. In addition, the invention further provides a method for measuring algal settling rate by the settling algae collection device. The algae settling rate can be captured in situ in the field monitoring process, settling rules of different algae can be analyzed according to conditions of the different algae, and the method is of great significance for correctly understanding algal bloom formation and disappearance mechanisms and performing algal bloom prediction and forecast.