Noise figure (NF) and second harmonic distortion suppression ratio (2HD) are critical metrics for evaluating the performance of microwave photonic links. The NF characterizes the degradation of the signal-to-noise ratio and is primarily influenced by laser relative intensity noise, detector shot noise, and thermal noise. The 2HD reflects the limitation of nonlinear distortion on signal integrity. This paper proposes a dual-objective optimization method based on bias point adjustment to address the performance optimization of directly modulated microwave photonic links. The mapping relationships between the device parameters and link performance are theoretically analyzed based on establishment of a transfer model for the directly modulated optical link. Experimental measurements compare the NF and 2HD under different output power levels of the directly modulated laser. The results show that within the linear operation region of the laser, reducing the output power of a 1 550 nm wavelength laser improves the NF by 2.6 dB and maintains consistent link gain but deteriorates the 2HD by 2.44 dB. The study demonstrates a significant trade-off between the NF and harmonic suppression ratio, which necessitates dynamic selection of the optimal bias point based on practical application requirements. This work provides a foundation for flexible optimization of directly modulated links in communication, radar, and sensing systems.