This paper is a study, on small-scale Reynolds similarity criterion for model testof the trawl--net. After analysing the theoretical basis for current similaritycriteria, it gives a new similarity criterion based on small-scaled Reynolds similarity. 1. The main differences between the two kinds of criteria are as follows: (1) The current criteria do not consider the viscous force similarity. They supposethat the coefficient of net resistance is a constant, and the net resistance is proportionalto the square of velocity. In this criterion. we consider the coefficient of net resistanec (C_R) is not a constant but a function of Reynolds number, and then the viscous forcesimilarity criterion should be considered. (2) In the current criteria, the relation between the velocity of model net and fullscale net is introduced according to the gravity force similarity. But, according to thefilter-flow speciality of net, we think viscous force is the most important one for netresistance. We take the small-scaled Reynolds numbers similarity as a basis forintroducing the relation between the velocity of model net and full scale net. Simul-taneously, a revision coefficient (C₁) is introduced to consider the difference betweentwo large-scaled Reynolds numbers. 2. In this paper, the main points of the criterion are pointed out. The relationsbetween model net and full scale net are as follows: Large scale rstio: l₁/l₂ = b₁/b₂ =H₁/H₂=... = λ Small scale ratio: d₁/d₂ =a₁/a₂ = S₂'~(1/2)/S₂'~(1/2)=...=λ' Large-scaled Reynolds numbers: Re₁ = V₁l₁/v₁, Re₂ = V₂l₂/v₂ Small-scaled Reynolds numbers: Re₁' = V₁d₁/v₂, Re₂'= V₂d₂/v₂ The two small--scaled Reynolds numbers are equal: Re₁' = Re₂' The two large--scaled Regnolds numbers are not equal: Re₁≠Re₂ The relation between two velocities: V₂ = V₁λ' The formu1as of net resistance: R₁ = 1/2ρ₁V₁²Ω₁C(R₁), R₂ = 1/2ρ₂V₂²Ω₂C_(R₂) The relation between two resistance coefficients: C(R₁)=C₁C_R The coefficient C₂ is a revision coefficient. It considers the difference between twolarge-scaled Reynolds numbers. If Re₂'≥Re_(kp), C₁→1, Re_(kp) is a critical Reynolds number. In the above, "1" is for full scale net; "2" is for model net.