The invention discloses an excavator hydraulic system carrying a load sensing main valve and a positive flow pump, which comprises a main pump, a main valve with a main valve plug, a corresponding actuating element and an auxiliary element, wherein the excavator hydraulic system also comprises a regulating valve used for regulating the delivery of the main pump, the main pump is the positive flowpump, and the main valve is the load sensing main valve. Output flow of the main pump is compared with proper flow required by a working device, when the output flow of the positive flow pump is greater than the proper flow required by the working device, the output pressure of the regulating valve is reduced, the delivery control pressure of the main pump is decreased so that the delivery of thepositive flow pump is reduced, therefore, the output flow of the positive flow pump is reduced to reach the proper flow required by the working device. Respective partial advantages of a positive flow hydraulic system and a load sensing hydraulic system are combined in the invention, and flow of the pump is regulated in real time according to the magnitude of the load, thus the energy saving effect is better, and the characteristic of high response speed of the positive flow hydraulic system is inherited.