Landing leg hydraulic system, engineering machinery and control method of engineering machinery

The landing leg hydraulic system comprises an oil tank, an oil inlet oil way, an oil return oil way, a plurality of electromagnetic valve sets and a plurality of pairs of landing leg oil cylinders, any pair of landing leg oil cylinders comprises a horizontal oil cylinder and a vertical oil cylinder, and each electromagnetic valve set comprises a first electromagnetic valve and a second electromagnetic valve. The first electromagnetic valve comprises an oil inlet, an oil return port, a first oil port and a second oil port, the oil inlet is communicated with an oil inlet path, the oil return port is communicated with an oil return path, the first oil port is respectively communicated with a rod cavity of the horizontal oil cylinder and a rod cavity of the vertical oil cylinder through a first oil path, and the second oil port is connected with a second oil path; the first electromagnetic valve can control the extension or retraction of the supporting leg oil cylinder; the second electromagnetic valve is arrange