A hydraulic excavator, comprising: a main control valve, wherein the main control valve comprises: a straight travel valve unit , a rotary unit , a dozer blade unit , a first boom unit , a second boom and hammer unit , a first arm unit , a travel left unit , an oil inlet unit, a travel right unit , a bucket unit , a second arm unit , and an oil return passage (T2); the main control valve for hydraulic excavator is oil supplied by three pumps (P1, P2, P3) comprising a first pump (P1), a second pump (P2), and a third pump (P3), wherein the first pump (P1) and the second pump (P2) are two variable pumps having the same displacement and the third pump (P3) is standalone; the three pumps (P1, P2, P3) are under total power control, and the rated pressure of the third pump (P3) is less than the rated pressure of the first pump (P1) and that of the second pump (P2), characterized in that the main control valve for hydraulic excavator further comprises: a level-mode oil supply circuit, through which the first pump (P1), the second pump (P2) and third pump (P3) supply oil confluently to the arm cylinder of the hydraulic excavator, the level-mode oil supply circuit comprises: a level-mode selecting valve , the inlet of which is connected with the dozer blade unit , one outlet of which is connected with the second boom and hammer unit and another outlet of which is connected with the oil return passage (T2); a passage , one end of which is connected with the first arm unit and the other end thereof is connected with the bucket unit . a straight travel valve unit , a rotary unit , a dozer blade unit , a first boom unit , a second boom and hammer unit , a first arm unit , a travel left unit , an oil inlet unit, a travel right unit , a bucket unit , a second arm unit , and an oil return passage (T2); the main control valve for hydraulic excavator is oil supplied by three pumps (P1, P2, P3) comprising a first pump (P1), a second pump (P2), and a third pump (P3), wherein the first pump (P1) and the second pump (P2) are two variable pumps having the same displacement and the third pump (P3) is standalone; the three pumps (P1, P2, P3) are under total power control, and the rated pressure of the third pump (P3) is less than the rated pressure of the first pump (P1) and that of the second pump (P2), characterized in that the main control valve for hydraulic excavator further comprises: a level-mode oil supply circuit, through which the first pump (P1), the second pump (P2) and third pump (P3) supply oil confluently to the arm cylinder of the hydraulic excavator, the level-mode oil supply circuit comprises: a level-mode selecting valve , the inlet of which is connected with the dozer blade unit , one outlet of which is connected with the second boom and hammer unit and another outlet of which is connected with the oil return passage (T2); a passage , one end of which is connected with the first arm unit and the other end thereof is connected with the bucket unit . a level-mode selecting valve , the inlet of which is connected with the dozer blade unit , one outlet of which is connected with the second boom and hammer unit and another outlet of which is connected with the oil return passage (T2); a passage , one end of which is connected with the first arm unit and the other end thereof is connected with the bucket unit . <EOS>