A dense and crack free Ti-48Al-2Cr-2Nb alloy (TiAl alloy) with a height of 30 cm is prepared using laser melting deposition (LMD) method with preheating process, and the internal defects, microstructure, phase composition and mechanical properties of the alloy are studied. The micro/nano CT (computed tomography) testing results show that the density of the TiAl alloy formed after preheating is 99.996% and the number of pores is significantly less than that of the TiAl alloy formed without preheating. The microstructure of the sample is lamellar structure, metastable Weinstein structure, and feathery structure observed by optical microscopy and scanning electron microscopy. Only slight segregation of Cr and Nb elements is observed through energy spectrometer equipment. Electron back scatter diffraction experiment is conducted on the sample, and the main phase composition of the sample is γ phase, containing a small amount of α₂ and B2 phase. The average kernel average misorientation (KAM) value of TiAl alloy formed after preheating is slightly higher than that of the alloy formed without preheating. In addition the hardness and tensile properties of the dense and crack free alloy are tested, the alloy has a microhardness of 350 HV0.5, a tensile strength of 497 MPa, and an elongation of 0.49%. Its tensile properties are higher than those of traditional casting TiAl alloy. Therefore, the preheating process has important guiding significance for the LMD formation of high-density and crack free TiAl alloys.