Select one or more Y columns or a range of data from at least one Y column. If there is an associated X column, X column supplies X values; otherwise, sampling interval of the Y column or row number is used.
Select required data.
From the menu, select Plot > 2D: Line: Spline.
LINE.OTP (installed to the Origin program folder).
Each data point in the data plot is connected by a line. The line connection type is set to Spline on the Line tab of the Plot Details dialog box (Format: Plot).