Research conclusions: The adaptive genetic algorithms decides the cross location，cross rate and variance rate of chromosome based on the individual adaptive value in calculation process to make the cross moving to the algorithms convergence direction，which ensures the filial generation is better than father generation，make the start phase variable obviously and later phase stable slowly and ensure obtaining the optimal solution as a whole for population development，seeking balance and entire convergence．The optimal design of the trusses structure of the railway station canopy is made with the optimal design model for 3 D trusses and matlab software．The result shows the adaptive genetic algorithms is an ideal optimal design method for building structure．