The essentials and methods of determining the mesh size of trawlnets are discus-sed in this paper. The results of the practical tests indicate that the mesh size of traw-Inet, espa;ially in its front part, has direct and remarlable influence on trawlixgspeed. The trawling speed. hss not only important influence on fishing efficiency oftrawl gear, but also has a certain selection to the species and length of fish. Variousfish species adapt to different trawling speed, at optimum speed to certain species thehighest catch is achieved. Therefore, when、new trawlnet is designed, the mesh sizein front part of the net should be so determined that the trawlnet can reach to theimam speed. the horse power of vessels and dimensions of nets are in cnordinatian, themess size can be calculated. as follows:a₂=（V₂/V₁）^2.5·a₁where sign 1 and 2 separately show the prototype and the new trawlnet. Finally, thexnes.h size of some fish species is calculated and adapted to a existing trawlnet.