The invention discloses a Double GG composite channel base multi-hop-FSO bit error rate calculation method considering influence of different beam effects. The method comprises the following steps: 1)based on Double GG turbulence distribution, considering the influence of a point error and path loss, establishing a transmission model suitable for a multi-hop-FSO system; and on the basis, deducinga system probability density function and a cumulative distribution function under the joint action of the Double GG turbulence, the path loss and the point error; 2) obtaining a closed system bit error rate expression by using the Gaussian Laguerre polynomial, and performing simulation verification through a Monte Carlo method; and 3) considering the influence of different beams, substituting ahop count, normalized jitter, a normalized beam width and a weather condition parameter into a end-to-end closed average bit error rate expression of the multi-hop-FSO system to obtain the influence of the parameter on the performance of the multi-hop FSO system.