The LECR4 ion source (Lanzhou ECR ion source No.4) has been successfully put into service at IMP since February 2014. It includes the evaporative cooling magnets to provide the injection and an extraction magnet field. It is the first time for evaporative cooling technology used in ECR ion source in the world. According to the running of LECR4 in the following 4 years, the evaporative cooling technology can lead higher power density in coils and easy operation and maintenance. To increase the current density of coils and decrease the volume of magnet, the optimization analysis is taken in this paper, which includes the structure of coil unit and ion current in a constant magnet field of LECR4. The preliminary results of analysis show that the current density can be increased by 10% under a good cooling condition and the diameter of magnet can be decreased by 20%. The optimization is a condition of considerable improvements for LECR4 and other ion sources design.