The invention provides a cooling water jacket for a diesel engine. The cooling water jacket comprises a cylinder body, an air cylinder body water jacket, a piston, an air cylinder cover and an air cylinder cover water jacket; an air cylinder sleeve is arranged in the cylinder body, the air cylinder body water jacket is arranged on the outer side of the air cylinder sleeve, and the air cylinder body water jacket comprises a column body cold water cavity and a cooling pipe; the piston is arranged in the air cylinder sleeve, the air cylinder cover is arranged at the top end of the cylinder body,and the air cylinder cover water jacket is arranged in the position, directly facing a combustion chamber, of the air cylinder cover; and a water inlet hole is formed in the side wall of the air cylinder cover. According to the cooling water jacket, the high-temperature air cylinder sleeve and piston can be cooled through the air cylinder body water jacket, the cooling effect is good, the situation of cylinder breaking caused by uneven cooling can be avoided, the working efficiency of the diesel engine is improved, and the service life of the diesel engine is prolonged; and the combustion chamber can be cooled through the air cylinder cover water jacket, meanwhile, the uniformity of heat dissipation and cooling can be improved through an annular cold water cavity, a first annular cooling pipe and a second annular cooling pipe, and the situation of breaking of the air cylinder cover due to the local overheating or overcooling situation can be avoided.