Nanosized hemoglobin-based oxygen carriers are one of the most promising blood substitutes. In the present study, a comprehensive strategy for the preparation of nanosized cationic amylose-encapsulated hemoglobins (NCAHbs) was developed. First, cationic amylase (CA) was synthesized from amylose and quaternary ammonium salt by an etherification reaction. The structure of CA was characterized using Fourier transform infrared spectrophotometry (FTIR) and proton nuclear magnetic resonance spectrophotometry ((1)H NMR). The degree of substitution and the zeta potential were also measured. Then, the NCAHbs were prepared by electrostatic adhesion, reverse micelles and cross-linking. The UV-visible spectrophotometer was used to measure the entrapment efficiency (EE%) and drug loading efficiency (DL%) of the NCAHbs. Transmission electron microscopy and Malvern Nano-zs 90 analyzer were used to observe the size distribution and morphology of particles. Chemical structure was determined from the FTIR spectrum. A Hemox analyzer was used to measure the P(50) and Hill coefficients. A lethal hemorrhagic shock model in rats was used to evaluate the therapeutic effect of the NCAHbs. The results showed that the combined methods improved the size, stability, EE%, DL%, and oxygen-carrying capacity of the NCAHbs. The average diameter of the NCAHbs was 92.53 ± 3.64 nm, with a narrow polydispersity index of 0.027. The EE% was 80.05% ± 1.56% and DL% was 61.55% ± 1.41%. The P(50) and Hill coefficient were equal to 28.96 ± 1.33 mmHg and 2.55 ± 0.22, respectively. The size of NCAHbs remained below 200 nm for six days in PBS solution. The NCAHbs could effectively prevent lung injury from progressing to lethal hemorrhagic shock because they acted as both a volume expander and an oxygen carrier.