The invention discloses a construction site material weighing method and system, and the method comprises the steps: weighing all material transport vehicles by utilizing the advantages of small occupied area, convenient arrangement and rapid weighing of an axle load scale, and enabling the supervision range of a weighing management system to cover all the material transport vehicles; meanwhile, when the absolute value of 1-Q3/Q1 is less than or equal to the allowable deviation m, notifying a weighing controller to open a gate machine to enable the material transport vehicles to pass; when theabsolute value of 1-Q3/Q1 exceeds the allowable deviation m, notifying the material transport vehicles that the material transport vehicles has to pass through a precise weighing wagon balance so that the precise weight Q4 of the vehicles is obtained, calculating the on-site weight Q5 of the material, and taking Q5 as the material weight information in material management. According to the invention, the material weighing method achieves the automatic operation of the whole material weighing process through an informatization means, and achieves the optimization between the weighing efficiency and the weighing accuracy through combination of the axle load scale and the precise weighing wagon balance. The material weighing method has the advantages of full coverage of weighing supervision,high weighing operation efficiency, basis for deviation control and high automation control degree.