In this paper，the appearance of laser speckles in the experiment of measuring the refractive index

of plane glasses using laser as the optical source is described. A simple and effective suppression method of the laser

speckles is obtained. By using statistical rules，the factors influencing the contract of speckles are summarized from

analyzing the micro-beam interference field caused by laser diffusers. A staticrotated diffuser couple is chosen as

the reducer in the experiment，in which a static diffuser are added to increase the roughness of the incident laser

beam，and then the contrast of the speckles can be reduced to around 4% by using a rotating diffuser with a very

slow speed. As a result，very clear interference fringes can be observed at this situation.