Some improvements in the design of LDMOSFET power amplifier (PA) are demonstrated for effectively suppressing metallic shielding cover (MSC) effects. The internal and outer matching structures on the PCB are at first simulated and optimized using the commercial full-wave software HFSS. Further, they are integrated with the lumped-element circuit model of die and co-simulated using the software ADS 2013. With an Automation Testing Bench employed, the input-output responses of the realized PA modules are measured and compared. An improved design of the LDMOSFET die is also presented and validated. This research can provide some useful guidelines for the development of PA modules with high performance.