High-strength sheet including 2MnB5 Boron and magnesium alloy sheet is the material commonly used in modern machinery, which is easy to induce problems such as excessive rebound, cracking, forming force increase, easy mould wear and the like. The heat analysis of 2MnB5 Boron and magnesium alloy sheet hot stamping forming process and experiments indicate that the transition process from Austenite to Martensite by controlling the sheet heating and cooling temperature is the foundation of heat forming. Only when the cooling rate reaches or surpasses the critical cooling rate, Austenite can be transformed to Martensite directly. Critical cooling rate of sheet is related to the elements of critical water flow rate, mould cooling system design, cooling medium, dented mould medium and the like. Under the condition that the elements of mould structure, cooling system, cooling medium and the like are defined, critical cooling rate is a constant value. As a result, through controlling critical water flow rate, hot forming transition process and hot forming requirements can be guaranteed to overcome the excessive rebound, cracking, forming force increase, easy mould wear and the like in hot forming process.