Abstract: This paper analyzed the high-speed microprojectile velocity regained in the gene-gun techniques to penetrate into plant cell with foreign gene, three dynamic processes were investigated: the projection of the microprojectile, the acceleration of the projectile, and tile plant cell penetration. Spring regidity of the gene-gun was suggested, and a method for determining the microprojectile projecting velocity by combining theoretical analysis with experimantal measurement was proposed, and tile minimum velocity of the microjectile required to penetrate into plant cell was established, and thus a theoretical ground for the design of the gene-gun was provided.