Abstract: Abstract: Using some different ways to strength the local heat transfer ability of diesel cylinder head has some research productions, such as optimization of cooling fluid flow path, using more efficient cooling liquid, and using split cooling systems to meet demands of different positions of diesel engine. However, the effect of the first method seems limited, the results of the second method have been notoriously divergent, and the original intention of the third method is to increase intake flow. Some researchers put forward an idea that uses the nanofluids with jet impingement technology to improve the performance of heat transfer of diesel engine cylinder head, but this method has high energy consumption and cylinder head has been changed big too much. This paper attempts to use magnetic nanofluids with external alternation magnetic field to improve the heat transfer performance of diesel cylinder head at nose bridge area, based on two main reasons, one is nanofluid coolant has good heat transfer characteristics and the other is magnetic field changing enhances the nanometer particle moving trend. Based above reasons, this paper made some basic researches aiming to find out whether external alternative magnetic field can better improve moving trend of magnetic nanometer particles or not, furthermore, applying the above basic research results to a diesel with split-type cooling system to explore whether external alternative magnetic field can improve the heat transfer performance of diesel engine cylinder head or not, using traditional glycol, Cu-glycol nanofluid coolant and magnetic Fe3O4 nanofluid coolant, respectively. The results of this study showed, with the effect of external alternation at 0.17 Hz frequency, the eddy number of magnetic nanofluid coolant was increasing obviously and the heat transfer performance of nanofluid coolant was improved, and the biggest incline range of temperature value of heating rod was caused, which was 17.2%. The temperature test of cylinder head bottom showed that, compared with traditional glycol coolant, under steady operating condition, the maximum declines of the temperature values in the maximum torque point and the calibration operation point were 11.6% and 14.4%, respectively, and the average temperature decline of external characteristics operating point was 23.7 ℃, around 9.4%. The test results of transient condition showed that, compared with traditional glycol coolant or Cu-glycol nanofluid coolant, using magnetic nanofluid coolant with external alternative magnetic field at 0.17 Hz frequency, the tested diesel engine preheating time were reduced by 9.8% and 8.2%, respectively, and the coolant temperature fluctuation was relatively small. Of course, the above research results were obtained in the appropriate measures for test diesel engine. The energy consumption calculation results showed that, at the same cooling effect of test diesel engine cylinder head tiny area, compared with using traditional glycol coolant, the energy-saving rate was 7.2% when using magnetic nanofluid coolant with external alternative magnetic field at 0.17 Hz frequency. The purpose of this study is to explore the basic application method to strengthen local cooling ability on high temperature area such as diesel engine, and to provide a scientific reference of energy saving and less change for cylinder head structure.