An automatic biochemical analyzer is provided, the analyzer includes a reaction wheel that comprises an inner ring and outer ring, an interval of a photoelectric detection position of the inner ring and that of the outer ring is N cuvette positions along counterclockwise or clockwise direction, and an interval of a sample injecting position, a reagent injecting positions, a sample stirring position and a reagent stirring position of the inter ring and those of the outer ring respectively is M cuvette positions along the same direction, wherein M and N are integers and the difference between M and N is 0 or 1. The analyzer at the premise of ensuring the test flow, reducing wasting number of cuvettes, saving the cost of the whole analyzer, and the size of the reaction wheel will be as small as possible.