The invention provides a bath dyeing and color fixing method of a polyamide fabric. The method includes the steps: adding staining fluid into the polyamide fabric to be dyed, heating mixture at constant speed to reach the temperature of 80-100 DEG C to dry the polyamide fabric to be dyed; cooling the mixture to reach the temperature of 50-75 DEG C after dyeing to fix a color, and adding a color fixing agent in the color fixing process to obtain the dyed polyamide fabric. The staining fluid comprises acid dyes and additives. According to the method, dyeing and color fixing in the dyeing processof the fabric are synchronously implemented, operation processes are simplified, dyeing energy consumption is reduced, dyeing time is saved, knitted fabric can be uniformly dyed by a dyeing and colorfixing process in the method, fastness effects are good, color difference is less, and colors are stable.