The D200 straw fiber extruder developed by Northeast Agricultural University is used mainly in fiber processing to get crop straw expanded by utilizing physical extrusion method, which can realize clean, efficient and high value utilization of crop straw. In order to improve the efficiency in soaking, cleaning, continuous and stable conveying of crop straw material and solve the problems of strong labor intensity when it is fed artificially and nonuniformly, the development of a matched raw material supply device is absolutely necessary. This supply device mainly consisted of soaking device, stirring device and fishing conveyor device, in which the fishing conveyor device functions as a critical component. Based on analysis of the cooperating relationship among three systems (referring to soaking, stirring and fishing systems), a fishing rake was selected as research object to establish a mathematical model of fishing amount by analyzing the kinematic process between harrow tooth and straw. Belt linear velocity, harrow tooth number and rotating speed of agitator were proved to be the effective factors affecting fishing efficiency. Critical condition that the straw was not thrown out from harrow was found through force analysis when straw was separated from the water surface. The test material was Dongnong No.425 rice straw. Experimental investigations were carried out with the method of L16 (45) orthogonal test to obtain the optimal parameter combination. Meanwhile, the belt linear velocity, harrow tooth number and rotating speed of agitator were supposed to be the main influence factors. Fish efficiency and variable coefficient of fishing efficiency were chosen as the evaluating indicator. The results showed that belt linear velocity, harrow tooth number and rotating speed of agitator had very significant effect on fishing efficiency （P<0.01);belt linear velocity had very significant effect on variation coefficient of fishing efficiency （P<0.01). Subsequently, by using fuzzy comprehensive evaluation method, the order of the comprehensive indicator combined fishing amount with variation coefficient of fishing efficiency was the belt linear velocity, the harrow tooth number and the rotation speed of agitator. The optimal combination of parameters occurred with linear velocity of conveyor line at 0.6m/s, rotation speed of stirring paddle at 40r/min, harrow tooth number of rake of 8 when fishing amount per unit time was 1111.2kg/h and variation coefficient was 0.124. This research provided a reference for the structural improvement of the supply system of raw crop straw and guidance for the optimization of the operating parameters as well.