The tubular flocculation reactor is a new device for the efficient treatment of algal wastewater, which has the characteristics of high removal efficiency and small dosage of chemicals. The mechanism of the influence of the flow field on the formation of floc in the pipeline has not been clarified. In this study, the effects of flow field distribution, reagent concentration and algal concentration on removal efficiency were investigated by means of experiment and numerical simulation. The results showed that the removal efficiency of the surface tubular flocculation reactor was related to the shape of the generated floc. When the size of the generated floc was greater than 900µm and the fractal dimension was greater than 1.25, the removal efficiency of the tubular flocculation reactor exceeded 90%, and the removal efficiency of the tubular flocculation reactor could eventually reach more than 98% with continued increase of the floc size and compactor degree. Under the same pipe diameter, the size and fractal dimension of flocs are linearly correlated with the proportion of inertial subregions in the flow field. After the flow rate is increased from 0.15m·s^-1 to 0.3m·s^-1, the non-positive region of Q criterion in the pipeline is reduced by 3%, the size of flocs is reduced by 200µm, and the fractal dimension is decreased by 0.3.