A subwavelength electromagnetic diode scheme in a microwave waveguide system is proposed by using an asymmetric photonic crystal (PC) cavity side-coupled with electromagnetically induced transparency like (EIT-like) metamaterials. It is found that the composite PC-EIT configuration can generate tenfold Q-factor enlargement, accompanied with enhanced nonreciprocal electromagnetic localization simultaneously. Further study of the measured one-way response exhibits excellent electromagnetic diode performance including 19.7 dB transmission contrast and 7 dBm operating power at a working frequency of 1.329 GHz. We emphasize that such high-contrast transmission and low-threshold diode actions are not at costs of greatly increasing volume and drastically reducing transmission. Our findings may benefit the design of compact nonreciprocal devices in the integrated optical nanocircuits.