use this :
void AddConstructor(TypeDefinition type, MethodReference baseEmptyConstructor)
{
var methodAttributes = MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName;
var method = new MethodDefinition(".ctor", methodAttributes, ModuleDefinition.TypeSystem.Void);
method.Body.Instructions.Add(Instruction.Create(OpCodes.Ldarg_0));
method.Body.Instructions.Add(Instruction.Create(OpCodes.Call, baseEmptyConstructor));
method.Body.Instructions.Add(Instruction.Create(OpCodes.Ret));
type.Methods.Add(method);
}
you can also refer :