A continuous testing method for testing the concentration of a target object in a fluid is provided. The method comprises the following steps. A focused light is provided in the fluid to separate the target object from a non-target object in the fluid by changing the movement direction of the target object and the non-target object. The fluid having separated out the non-target object is enabled to react with a reagent. A signal is provided to pass through the fluid having reacted with the reagent. The signal passing through the fluid is received and an electronic signal is outputted corresponding to the input signal. The concentration of the target object is acquired according to the electronic signal.