The invention relates to a road slope computation method based on road alignment and spectrum features and solves the problems that road slope information in existing automobile operation work condition design quite depends on GPS (global position system) signals, has large errors and cannot be applied to operation work condition design. The road slope computation method comprises the following steps: 1, acquisition of data and establishment of an original database Database; 2, data processing: data in the original database Database is underclocked, altitude values at idling moments are all set to be hidle, a traveling segment is divided into a plurality of micro-travels, and the micro-travels with a micro-travel distance smaller than a set limit value smin are combined in adjacent micro-travels; 3, computation of slope-mile i3-s3 in the micro-travels; 4, conversion of a slope-time i4-t4 sequence: slope-mile i3-s3 data computed in the step 3 in the micro-travels are combined, and the whole slope-mile i4-s4 data formed after combination is converted into slope-time i4-t4 data to be output according to mile-time s1-t1 data of a vehicle.