The work aims to explore the new laser cladding process of TiN/Ti-Al-Nb composite coatings on Ti6Al4V titanium alloy surface and study the influence laws of Nb content on microstructure and microhardness of TiN/Ti-Al-Nb composite coatings. The mixed powder of Ti, Nb and AlN with 10%, 15% and 25% Nb was used as raw materials to prepare TiN/Ti-Al-Nb composite coatings on Ti6Al4V alloy surface by in-situ synthesis assisted laser cladding based on extrusion presetting powder method. XRD phase qualitative analysis method, SEM and EDS were used to carry out qualitative analysis on the phase of TiN/Ti-Al-Nb composite coatings. According to the binary equilibrium phase diagram, the laser in-situ chemical reaction mechanism was analyzed further. With the help of microhardness tester, the influence laws of the microstructure of TiN/Ti-Al-Nb composite coatings on the cross-sectional microhardness distribution were studied. Under the high energy density laser beam, only Ti and AlN had sufficient laser in-situ chemical reaction to form TiN ceramic reinforcement. The content of TiN was positively correlated with the content of Ti powder and AlN powder. The increase of Nb content significantly affected the types of Ti-Al-Nb phases, but not changed the types of reinforcements. With the increase of Nb content, the types of Nb phases increased and transformed as follows: Ti3Al→Ti3AlNb→Ti2AlNb→Ti39Nb→Nb7Al. The average microhardness of the cross-section of the composite coating decreased from 993.2HV0.5 to 701.4HV0.5 with the decrease of TiN reinforcement. The increase of Nb content does not change the type of reinforcement of the composite coating, but can reduce the content of TiN reinforcement, thus reducing the average microhardness of the composite coating section.